FEAT: Handle private git repositories with native mechanism

[nieomylnieja]

Since the shortcomings of go list are rendering it hard/impossible to use in some scenarios, we want to bridge the last gap between our raw GOPROXY (default) approach and go list.

The solution will require us fetching a remote repository, cloning it in a temporary (or not?) directory and reading the git tags.
Support of other VCS is left out.