Add git hashes to commits metadata

[lutien]

Extracted the part about adding the git hashes to commits metadata from #2658.

• I got the information that there is a CSV file with mapping between git and hg hashes up until the git migration data of last year. For the rest, we have to use the API. My idea would be to use this file as a starting point and then continue writing to it with new hashes.

[jgraham]

Is there a reason to to add the mapping to the per-commit metadata in the repository (i.e. the git notes for each commit), and read that? We could consider a one-time import of the CSV file to backfill existing data (but that could be overkill; I think it's pretty likely we ~never read these older commits, unless I'm forgetting something).

[jgraham]

I think the naming here is getting confusing because for mozilla-central we have three different possible revisions, two of which are git. Maybe we should call it canonical_rev_git. Here the implementation would look like:

@property
def canonical_rev_git(self) -> str:
    if self.cinnabar:
        raise ValueError(f"Commit {self.sha1} doesn't have a canonical git SHA1")
    return self.sha1

But then in GeckoCommit you'd override it to:

@property
def canonical_rev_git(self) -> str:
    if self.cinnabar:
        if "gecko-commit-git" not in self.notes:
            self.notes["gecko-commit-git"] = hg2git(self.sha1)
        sha1 = self.notes["gecko-commit-git"]
        assert sha1 is not None
        return sha1
    return self.sha1

[lutien]

Ok, updated