feat: add github_actions_organization_secret_repository resource

[ylascombe]

Resolves #2759

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Before the change?

Currently, the GitHub Terraform provider allows managing GitHub Actions secrets within your GitHub organization with github_actions_organization_secret resource,
it also allow to manage repository allow list for existing GitHub Actions secrets within your GitHub organization with actions_organization_secret_repositories

What is currently available:

resource "github_actions_organization_secret_repositories" "org_secret_repos" {
  secret_name = "existing_secret_name"
  selected_repository_ids = [
    123455,
    234567,
    345678,
  ]
}

After the change?

The provider do not yet allow to select/allow or unselect only one repo in the selected repos list.

Manage repo selection for organization secret can be useful when:

• the terraform stack use do not known/manage all the repositories of the organization
• we want to manage only a repository and we do not want to alter the other assignment.

So I propose in this PR to add a new resource to manage the addition (selection) or removal (unselection) for a GitHub Action Organization secret for a repo
Example

data "github_repository" "this" {
  full_name = "myorg/myrepo"
}

resource "github_actions_organization_secret_repository" "org_secret_repos" {
  secret_name = "EXAMPLE_SECRET_NAME"
  repository_id = github_repository.internal.repo_id
}

This feature would align with the GitHub API capabilities, where you can assign organization secrets:

• either to all repos: https://docs.github.com/en/rest/actions/secrets?apiVersion=2022-11-28#set-selected-repositories-for-an-organization-secret
• or only a repo: https://docs.github.com/en/rest/actions/secrets?apiVersion=2022-11-28#add-selected-repository-to-an-organization-secret

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

No

Please see our docs on breaking changes to help!

• Yes
• No

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