feat: Align environment branch policy support

[stevehipwell]

Resolves #1997

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Before the change?

There was duplication between the github_repository_environment_deployment_policy & github_repository_deployment_branch_policy resources and no way to look up tag based deployment policies.

After the change?

I've added a new github_repository_environment_deployment_policies data source to support looking up tag based deployment policies as well as branch based ones. I've deprecated the github_repository_deployment_branch_policy resource and the data_source_github_repository_deployment_branch_policies to be removed in the next major release.

Pull request checklist

• Schema migrations have been created if needed (example)
• 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?

Please see our docs on breaking changes to help!

• Yes
• No

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[nickfloyd]

❤️