Don't force new argocd_application_set resource when adding/removing match_expressions

[ahublersos]

Fixes (#330).

This PR removes ForceNew: true from the matchExpressionsSchema() allowing match expressions to be added and removed without destroying the argocd_application_Set resource.

After making the changes, I see a handful of tests failing. Some, like TestAccArgoCDRepositoryCertificatesSSH_WithApplication, TestAccArgoCDRepositoryCredentials, and TestAccArgoCDApplicationSet_matrixInvalid fail even without the changes in this PR. TestAccArgoCDApplicationSet_mergeInvalid and TestAccArgoCDApplicationSet_generatorTemplate begin failing once ForceNew: true is removed and I can't seem to figure out how they are connected tomatchExpressionsSchema().

Here are the test failures:
--- The first two tests only fail once ForceNew: true has been removed from matchExpressionsSchema().

=== CONT  TestAccArgoCDApplicationSet_mergeInvalid # Not present without change
    resource_argocd_application_set_test.go:718: Step 1/3, expected an error with pattern, no match on: Error running pre-apply refresh: exit status 1

        Error: Not enough list items

          on terraform_plugin_test.tf line 9, in resource "argocd_application_set" "merge_insufficient_generators":
           9: 			merge {

        Attribute spec.0.generator.0.merge.0.generator requires 2 item minimum, but
        config has only 1 declared.
--- FAIL: TestAccArgoCDApplicationSet_mergeInvalid (0.91s)

=== CONT  TestAccArgoCDApplicationSet_generatorTemplate # Not present without change
    resource_argocd_application_set_test.go:739: Step 1/2 error: Error running apply: exit status 1

        Error: failed to create application set generator-template

          on terraform_plugin_test.tf line 2, in resource "argocd_application_set" "generator_template":
           2: resource "argocd_application_set" "generator_template" {

        rpc error: code = Internal desc = grpc: failed to unmarshal the received
        message: unexpected EOF
--- FAIL: TestAccArgoCDApplicationSet_generatorTemplate (7.17s)

--- The tests below fail every time, even running from master with no changes.

=== RUN   TestAccArgoCDRepositoryCertificatesSSH_WithApplication
    resource_argocd_repository_certificate_test.go:207: Step 1/1 error: After applying this test step, the plan was not empty.
        stdout:


        An execution plan has been generated and is shown below.
        Resource actions are indicated with the following symbols:
          ~ update in-place

        Terraform will perform the following actions:

          # argocd_repository.private will be updated in-place
          ~ resource "argocd_repository" "private" {
                id                      = "git@private-git-repository.argocd.svc.cluster.local:~/project-1.git"
              - username                = "git" -> null
                # (6 unchanged attributes hidden)
            }

        Plan: 0 to add, 1 to change, 0 to destroy.
--- FAIL: TestAccArgoCDRepositoryCertificatesSSH_WithApplication (42.53s)

=== RUN   TestAccArgoCDRepositoryCredentials
    resource_argocd_repository_credentials_test.go:19: Step 4/4 error: After applying this test step, the plan was not empty.
        stdout:


        An execution plan has been generated and is shown below.
        Resource actions are indicated with the following symbols:
          ~ update in-place

        Terraform will perform the following actions:

          # argocd_repository.private[0] will be updated in-place
          ~ resource "argocd_repository" "private" {
                id                      = "git@private-git-repository.argocd.svc.cluster.local:~/project-1.git"
              - username                = "git" -> null
                # (6 unchanged attributes hidden)
            }

          # argocd_repository.private[1] will be updated in-place
          ~ resource "argocd_repository" "private" {
                id                      = "git@private-git-repository.argocd.svc.cluster.local:~/project-2.git"
              - username                = "git" -> null
                # (6 unchanged attributes hidden)
            }

          # argocd_repository.private[2] will be updated in-place
          ~ resource "argocd_repository" "private" {
                id                      = "git@private-git-repository.argocd.svc.cluster.local:~/project-3.git"
              - username                = "git" -> null
                # (6 unchanged attributes hidden)
            }

          # argocd_repository.private[3] will be updated in-place
          ~ resource "argocd_repository" "private" {
                id                      = "git@private-git-repository.argocd.svc.cluster.local:~/project-4.git"
              - username                = "git" -> null
                # (6 unchanged attributes hidden)
            }

          # argocd_repository.private[4] will be updated in-place
          ~ resource "argocd_repository" "private" {
                id                      = "git@private-git-repository.argocd.svc.cluster.local:~/project-5.git"
              - username                = "git" -> null
                # (6 unchanged attributes hidden)
            }

          # argocd_repository.private[5] will be updated in-place
          ~ resource "argocd_repository" "private" {
                id                      = "git@private-git-repository.argocd.svc.cluster.local:~/project-6.git"
              - username                = "git" -> null
                # (6 unchanged attributes hidden)
            }

          # argocd_repository.private[6] will be updated in-place
          ~ resource "argocd_repository" "private" {
                id                      = "git@private-git-repository.argocd.svc.cluster.local:~/project-7.git"
              - username                = "git" -> null
                # (6 unchanged attributes hidden)
            }

          # argocd_repository.private[7] will be updated in-place
          ~ resource "argocd_repository" "private" {
                id                      = "git@private-git-repository.argocd.svc.cluster.local:~/project-8.git"
              - username                = "git" -> null
                # (6 unchanged attributes hidden)
            }

          # argocd_repository.private[8] will be updated in-place
          ~ resource "argocd_repository" "private" {
                id                      = "git@private-git-repository.argocd.svc.cluster.local:~/project-9.git"
              - username                = "git" -> null
                # (6 unchanged attributes hidden)
            }

          # argocd_repository.private[9] will be updated in-place
          ~ resource "argocd_repository" "private" {
                id                      = "git@private-git-repository.argocd.svc.cluster.local:~/project-10.git"
              - username                = "git" -> null
                # (6 unchanged attributes hidden)
            }

        Plan: 0 to add, 10 to change, 0 to destroy.

=== CONT  TestAccArgoCDApplicationSet_matrixInvalid
    resource_argocd_application_set_test.go:262: Step 1/4, expected an error with pattern, no match on: Error running pre-apply refresh: exit status 1

        Error: Not enough list items

          on terraform_plugin_test.tf line 9, in resource "argocd_application_set" "matrix_insufficient_generators":
           9: 			matrix {

        Attribute spec.0.generator.0.matrix.0.generator requires 2 item minimum, but
        config has only 1 declared.
--- FAIL: TestAccArgoCDApplicationSet_matrixInvalid (1.00s)

[ahublersos]

Looks like all the tests that were failing locally are passing in the automated PR acceptance tests.

[onematchfox]

@ahublersos, thanks so much for taking the time to put together this PR (and sorry for the strange issues you seem to be having).

FWIW, I had been debating whether to make ForceNew configurable as per the Kubernetes provider but since it doesn't need to be set to true in this provider I think we can leave that for another day.

Re, the failing tests: yeah, this seems weird. Have relaunched the failed actions and if all passes I'll happily approve and merge this change.

[ahublersos]

@ahublersos, thanks so much for taking the time to put together this PR (and sorry for the strange issues you seem to be having).

FWIW, I had been debating whether to make ForceNew configurable as per the Kubernetes provider but since it doesn't need to be set to true in this provider I think we can leave that for another day.

Re, the failing tests: yeah, this seems weird. Have relaunched the failed actions and if all passes I'll happily approve and merge this change.

@onematchfox Thanks for sharing that link to the Kubernetes provider, I hadn't seen that pattern before. TIL!