fix: Defaults the role_name coalesce to * to workaround import error

[mike-carey]

Description

Defaults the role_name to * within the coalesce to workaround #83. By setting a dummy value as the default option, terraform can successfully import without erroring out because the variables are empty and null. If one still forgot to set both values, an error will be thrown when attempting to create any of the IAM resources with the * value.

Error: invalid value for name (must match [\w+=,.@-])

  on .terraform/modules/application.lambda/iam.tf line 71, in resource "aws_iam_policy" "logs":
  71:   name   = "${local.role_name}-logs"

Motivation and Context

We still use terraform 0.12 and would like to upgrade to at least v1.29.0 at least up to v1.39.0. See #83 for details involving the current issue.

Breaking Changes

No breaking changes. If anyone is using v1.39.0, it is locked to terraform 0.13 anyways and it seems this bug is specific to 0.12. However, I wanted to put this out there in anticipation of potentially reverting the minimum version to 0.12.

How Has This Been Tested?

• I have tested and validated these changes using one or more of the provided examples/* projects

When using the versions of the module anywhere from v1.29.0 to v1.38.0, I attempted to import resources only to result in the error specified in #83. When changing the terraform file directly, (editing .terraform/modules/lambda/iam.tf), the import then works. Commenting out the function name and role name being passed in results in the validate error above.

[antonbabenko]

Thanks for the PR!

The minimum version of Terraform is reverted to 0.12.26 in #117 and available in v1.40.0 of this module, so this PR is relevant for the master branch I believe.

[antonbabenko]

v1.43.0 has been just released.

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