Add necessary arguments/resource to be able to restrict branches for pull and push mirrors

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Hello 👋

New Resource

On the UI, it is possible to restrict mirroring (pull and push) on specific branches, using a regular expression. For now, it seems the provider only supports the "Mirror only protected branches" option, but not the ability to input a regular expression.

For example, for push mirrors:

resource "gitlab_project_mirror" "foo" {
  project = "1"
  url     = "https://username:password@github.com/org/repository.git"

  # This would be mutually exclusive with `only_protected_branches`.
  only_specific_branches = "^feature/.*$"
}

For example, for the pull mirror:

resource "gitlab_project" "foo" {
  […]

  # This would be mutually exclusive with `only_mirror_protected_branches`.
  only_mirror_specific_branches = "^feature/.*$"
}

Related GitLab APIs

https://docs.gitlab.com/ee/api/projects.html#configure-pull-mirroring-for-a-project

https://github.com/xanzy/go-gitlab/blob/main/project_mirror.go#L43

Additional Details

Edited by 🤖 GitLab Bot 🤖