How we let internal teams with no public repo urls to use cargo-crev

[dpc]

I think we need to support that use-case, even if the main effort is for public collaboration.

Here is what I think RN:

I was thinking how teams internally collaborate when they use github for private repos and we probably just want to embrace ssh-accessible private repositories in the same fashion. Users would just either share one repo, or push to their own forks and submit PRs to their main repository that they have otherwise RO access.

The cargo crev repo fetch would just not cover that use-case. We could make a possibility of no public URL on the PublicId, while preserving an ability to create proofs, run cargo crev repo git <git command>, and push things.

@kornelski I know you did some push into using cargo-crev without an ID yet front. Does this fit with your vision?