Add workflows to check base branch and set stable branch

[oliverholworthy]

Part of https://github.com/NVIDIA-Merlin/Merlin/issues/866

Goals :soccer:

• Ensure the base branch of PRs is the development branch. (check-base-branch.yaml)
• Update the stable branch to correspond with the latest release tag (set-stable-branch.yaml) when a release is published or deleted

[github-actions[bot]]

Documentation preview

https://nvidia-merlin.github.io/Transformers4Rec/review/pr-694