[ci] Lint for "origin" lines in commit messages

[jwnrt]

This line indicates whether a commit is original to this branch or was cherry-picked from another.

It should be either:

• (commit is original to earlgrey_1.0.0)
• (cherry picked from commit <SHA>)

You can see the lint running here:
https://github.com/jwnrt/opentitan/actions/runs/11952913061/job/33319695210?pr=31

This PR also includes a commit hook for adding the "original" line in util/git/hooks/prepare-commit-msg.

[andreaskurth]

LGTM technically, though please hold off with merging until all TZs have had a chance to read the announcement email and reply in case of concerns.

Thanks @jwnrt!

[timothytrippel]

I would voice the opinion that having a special commit message for commit messages that originate on the earlgrey_1.0.0 branch is overkill and is going to cause a lot of toil for two reasons:

1. we don't do this on any other branch (including master), and
2. there is no hook to automatically apply it when working on one branch, but not apply it when working on another.

Also what value does it provide? I understand the value of the cherry-picked from ... message, and there is automation to apply this.

[andreaskurth]

Let's provide an automation for the (commit is original .. message on the dev side; please hold off until then. I'll follow up offline

[timothytrippel]

Thanks @jwnrt @andreaskurth; I discussed offline with @andreaskurth : I am OK with the commit message if there is a way for a git hook to automatically apply it based on what branch I am working on. Specifically, I am also OK if the target branch needs to be specified on the command line once per branch I create, e.g.,

git checkout -b contribution-to-bringup
git target-branch set earlgrey_1.0.0

[jwnrt]

I've added a commit hook. Instead of requiring an extra config step, it looks to see if the current branch is a descendent of earlgrey_1.0.0.

[timothytrippel]

awesome, thanks @jwnrt !