chore: add workflow for changelog label

[leogermani]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Adds a Workflow that will add a label and a comment to a PR after it's merged to trunk.

Context: pemhSX-De-p2

How to test the changes in this Pull Request:

Well, the only way to test it is merging :) Read the code

You can see how it looks like here

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[github-actions]

Hey @leogermani, good job getting this PR merged! 🎉

Now, the needs-changelog label has been added to it.

Please check if this PR needs to be included in the "Upcoming Changes" and "Release Notes" doc. If it doesn't, simply remove the label.

If it does, please add an entry to it to our shared document, with screenshots and testing instructions if applicable, then remove the label.

Thank you! ❤️

[matticbot]

🎉 This PR is included in version 5.7.0-alpha.1 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀

[matticbot]

🎉 This PR is included in version 5.7.0 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀