New github actions for conventional commits and generating release notes

[castrojo]

Hi everyone,

For those of you using ublue to make your own images ... I've added two new actions that you might want to incorporate into your own workflows:

release-please - this action will open a new pull request in your repo and start adding all the changes that you've merged into an in-progress changelog. When you're happy with the amount of work you've done merge the PR and then the bot will version, tag, and make a release. For my stuff here I'll likely set it to monthly so that there's an automatic cadence.

conventional-commits - the previous action only works if you're doing proper conventional commits, so I've added this action that will lint an incoming PR.

What I would love to figure out is a way to snag the changelogs from: rpm-ostree db diffs --changelog and incorporate that here, but it's a start. Enjoy!