[Github workflow] Add new tag on version.py update

[constanca-m]

What does this PR do?

It adds two GitHub actions workflows:

• changelog: when version.py is updated on a pull request, it will check if CHANGELOG has the first line with * v$VERSION*
• release: When share/version.py gets pushed, it will automatically create a new tag named lambda-v{VERSION}.

Why is it important?

It automates the tag process as mentioned in https://github.com/elastic/elastic-serverless-forwarder/issues/540.

With this workflow, we can also create a new workflow to zip dependencies on a new tag creation like mentioned in the issue https://github.com/elastic/elastic-serverless-forwarder/issues/683.

Checklist

• [ ] My code follows the style guidelines of this project
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have made corresponding change to the default configuration files
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added an entry in CHANGELOG.md

Related issues

• Relates https://github.com/elastic/elastic-serverless-forwarder/issues/540.
• Relates https://github.com/elastic/elastic-serverless-forwarder/issues/683.

[girodav]

Have you considered a different approach, like updating version.py when a git tag is created instead? (see Tom's comment here).

Regardless of the approach, I'd also make sure that also CHANGELOG.md is updated before releasing.

[constanca-m]

Thanks @girodav. I added a changelog workflow. I will leave the version.py as the trigger, as it does not seem to make much difference.