Add new rules to Channels to enable protection of Git resources

[geofflamrock]

We are adding new rules to Channels to better support deployments which use Git repositories, allowing you to ensure that only the intended Git resources are used when deploying to protected environments such as Production. These will include new rules for:

• The branches or tags which can be used as the source of the deployment process when creating releases for version controlled projects.
• The branches or tags which can be used when creating releases that source files from external Git repositories, for example sourcing scripts or Kubernetes manifests.