Adds Gitlab provider

[dinosk]

Adds a Gitlab provider based on the one for github.
The mapping between Github and Gitlab entities:

Repo - Project
Org - Group
Team - Group

[stefanprodan]

@dinosk we need to change the client options and allow setting a different hostname for SSH, please see fluxcd/flux2#171

[dinosk]

we need to change the client options and allow setting a different hostname for SSH, please see fluxcd/toolkit#171

added an sshDomain field in https://github.com/fluxcd/go-git-providers/pull/36/files#diff-427f0edd6e28f8dd9251b1e762ca2b85R62 , will check if there is sth missing for this on the next iteration

[foot]

We should make a note here about which of these are expected to already exist vs. will be created

[foot]

Added comment.

[foot]

this seems to need the https:// prefix to work w/ other domains.

[foot]

But as we're not really passing scheme around maybe the NewClient should append it

[foot]

Added a comment.

[foot]

Works! sans the caching request, our gitlab instance doesn't support that.

$ ginkgo gitlab
Running Suite: GitLab Provider Suite
====================================
Random Seed: 1600782102
Will run 10 of 10 specs

• Failure [3.214 seconds]
GitLab Provider
/Users/simon/src/go-git-providers/gitlab/integration_test.go:125
  should list the available organizations the user has access to [It]
  /Users/simon/src/go-git-providers/gitlab/integration_test.go:200

  Expected
      <int>: 0
  to equal
      <int>: 1

  /Users/simon/src/go-git-providers/gitlab/integration_test.go:246
------------------------------
•••
------------------------------
• [SLOW TEST:5.222 seconds]
GitLab Provider
/Users/simon/src/go-git-providers/gitlab/integration_test.go:125
  should update if the org repo already exists when reconciling
  /Users/simon/src/go-git-providers/gitlab/integration_test.go:301
------------------------------
• [SLOW TEST:16.630 seconds]
GitLab Provider
/Users/simon/src/go-git-providers/gitlab/integration_test.go:125
  should update teams with access and permissions when reconciling
  /Users/simon/src/go-git-providers/gitlab/integration_test.go:344
------------------------------
• [SLOW TEST:6.614 seconds]
GitLab Provider
/Users/simon/src/go-git-providers/gitlab/integration_test.go:125
  should create, delete and reconcile deploy keys
  /Users/simon/src/go-git-providers/gitlab/integration_test.go:439
------------------------------
• [SLOW TEST:10.660 seconds]
GitLab Provider
/Users/simon/src/go-git-providers/gitlab/integration_test.go:125
  should be possible to create a user project
  /Users/simon/src/go-git-providers/gitlab/integration_test.go:501
------------------------------
•
------------------------------
• [SLOW TEST:14.436 seconds]
GitLab Provider
/Users/simon/src/go-git-providers/gitlab/integration_test.go:125
  should update if the user repo already exists when reconciling
  /Users/simon/src/go-git-providers/gitlab/integration_test.go:545
------------------------------
Deleting the user repo:  test-repo-194
Deleting the org repo:  test-org-repo-217
Deleting the shared org repo:  test-shared-org-repo-812


Summarizing 1 Failure:

[Fail] GitLab Provider [It] should list the available organizations the user has access to
/Users/simon/src/go-git-providers/gitlab/integration_test.go:246

Ran 10 of 10 Specs in 67.313 seconds
FAIL! -- 9 Passed | 1 Failed | 0 Pending | 0 Skipped
--- FAIL: TestProvider (67.31s)
2020/09/22 15:42:53 GET https://gitlab.com/api/v4/groups/9146106: 401 {message: 401 Unauthorized}

Ginkgo ran 1 suite in 1m10.758218143s
Test Suite Failed

[foot]

LGTM :)

[dinosk]

Closing this, opened #51 to run the integration tests