Replace CodeCommit backend with other Git provider

[symroe]

CodeCommit is closing down

We need to move to a new git provider. We initially split up the repos per council because of CodeCommit bugs. We could re-visit this and have a single repo, but there might be some other advantages to having a repo per council.

Things to consider, but either way we should move away from CodeCommit, even though they're continuing to support it for existing customers.