PLAYNEXT-500 Check pull request labels

[pyby]

Description

The workflow documentation mentionnes to add a label to any PR, to help tag release notes.
A GitHub Action can check that allowed labels are used.

Changes Made

• Add a new GitHub action, which read allowed labels from .github/release.yml and compare with the labels on PR.
• Update documentation to mentioned GitHub actions.

Checklist

• I have followed the project's style guidelines.
• I have performed a self-review of my own changes.
• I have made corresponding changes to the documentation.
• My changes do not generate new warnings.
• I have tested my changes and I am confident that it works as expected and doesn't introduce any known regressions.
• I have reviewed the contribution guidelines.