Add Github Action workflow for release notes generation

[jsvd]

This change takes the existing release notes draft generator script and wraps it into a GH action workflow.

The workflow just runs the script, which is responsible for computing the draft and creating a Pull Request.

The remaining changes are niceties:

1. instead of creating a PR titled "Release notes draft", create a "Release notes" draft PR
2. assign the PR to the person that executed the workflow, to facilitate tracking

Example: jsvd#6

[mashhurs]

LGTM!

I think your test settings still here, plz change your ID jsvd to elastic. Hope it is not by design Lol

[mashhurs]

👍