feat(meta 46): update CI to update CHANGELOG

[puckowski]

What:

Important: this will require standardizing commit headers. See formatting notes here: https://github.com/conventional-changelog/conventional-changelog/tree/master/packages/conventional-changelog-angular

Update Less.js GitHub CI with the capability to automatically update CHANGELOG.md on certain master pushes/PR merges.

Should resolve: less/less-meta#46

If a push or PR merge to master branch has a commit which has a header containing "Release v" the changelog CI will run and automatically commit changes to CHANGELOG.md.

Format:

On master push:
[commit header] ([commit hash])

On PR merge:
[commit header] ([PR link]) ([commit hash])

CHANGELOG.md sample:

Why:

Currently CHANGELOG.md maintenance is a manual effort which takes time and can be error prone.

Checklist:

• Documentation
• Added/updated unit tests
• Code complete

Should preserve historical CHANGELOG.md contents created via different means.

We can tweak the change formatting by adding a new configuration file, I went with the default angular style that did not require adding a configuration file.

[iChenLei]

Coooool