Adds github action to verify changelog entry and set milestone to PRs

[pseudo-nymous]

Description

Adds github action workflow to verify change log entry and set milestone based on the location of change log entry.

This workflow does the following step by step:

1. Check if the PR has skip changelog label to skip the further steps. Committers should add this label if they want skip adding change log entry. This is helpful when change log entry is not required.
2. Verifies if there is an entry in change log file (lucene/CHANGES.txt).
3. Extracts the milestone version based on the location of the change log entry.
4. Checks if the milestone exist in github then applies (adds/updates) the milestone version to the PR.
5. Flags if milestone version do not exist. Currently, we are only logging it. We can either add a comment to create the milestone or create one automatically if a new banner is created (=== Lucene XXX ===) under change log file.

Currently, I have only added logs in the action workflow testing all the flow. It's not blocking the merging process.
We can make it blocking based on the discussion in this PR.

Tested changes here: pseudo-nymous#13

Closes: #13898 #14190

[stefanvodita]

This is great work and really helpful @pseudo-nymous! I left some comments, but I'm looking forward to seeing this in action.

[dweiss]

Please do not force-push your changes. Keep prior commits so that the history is preserved and comments are attached where they should be. Thanks!

[pseudo-nymous]

There were small fixes which I missed in previous commit. This didn't had any history attached to it and I kept the commit which had comments.

Also, I'll keep this in check in next time. Thanks

[stefanvodita]

Thank you for making the changes @pseudo-nymous! I think once we make the action use the new label I created we're ready to test this out.

[pseudo-nymous]

I have updated the script to use new label. We are ready to test the changes.

[stefanvodita]

This looks good to me! If no one objects, I'll merge in the next few days and we can see how it runs. If we like what we see in the logs, we can come back and enable it to set milestones and comment on the PR.