Eliminate duplicate VCS processing - report shared VCSes

[szabgab]

There are several groups of crates wherein each group uses a single git repository. From the POV of the developer it is a monorepo, but from the POV of the crate user (and thus the digger) it means that several crates point to the same repo.

• When running git pull and when processing the data in the repos we should avoid doing it several times for the same repo. We should be able to reuse the results.

• We should probably also report which crates link to the same and verify if that is indeed correct or if the author mistakenly included the same repo-link in unrelated projects.