fetchcode take long time to download

[ziadhany]

sometimes we just need a small part of the repository like https://github.com/github/advisory-database
we just need to github-reviewed part 57.2 MB. but using fetch_via_vcs we download 2.00 GiB
the problem gets worth when we start rerunning the importer and debugging it,
at least we can have something like a cache for saving the repo so we can use it again.
https://github.com/github/advisory-database/tree/main/advisories/github-reviewed

aboutcode-org/vulnerablecode/issues/902