Add manual workflow to create Releases.

[pranavbhandari24]

The Dataflow templates team creates GitHub releases manually every Monday. This GitHub workflow can be used to automate part of this process and make it simpler for the team.

This workflow allows inputs of release branch name, tag name, branch commit, and any cherry pick commits to include. It creates a release branch with the branch commit and cherry-picks, and tags the latest commit of the release branch. It also makes a release with an empty notes section for the team to fill out. ( A future improvement can be to create the notes automatically).

[pranavbhandari24]

@an2x I created a GitHub workflow which can be used to reduce the time taken to create the releases on github. Please review.

[pranavbhandari24]

Currently, the workflow can only be triggered manually, but we can also schedule it each Monday if that works better.

[pranavbhandari24]

@zhoufek

[zhoufek]

LGTM - @damccorm just to verify.