Implement a mechanism to allow builds to leverage git describe

This is further technical debt introduced indirectly by #21 (closed) (!556 (merged)), as it was unacceptable to cache git repositories as a part of the build tree, and parallel work on using the build trees needed to be unblocked.

Background

More and more modules are using git describe at build time in order to derive their version number from the git history, this functionality is no longer working as of landing !556 (merged) for issue #455 (closed).

Task description

Need to find a way to allow modules to continue using git describe in the build sandbox, some research was done to allow staging of minimal history to allow this with the caveat of less determinism of builds, indeed having the .git history available alone introduces some non determinism.

Acceptance Criteria

Ideally, we have a mechanism where git describe works and builds are entirely deterministic, but seeing as this is difficult to achieve and also that using git describe is very popular, a less than perfect approach of generating a condensed history when staging git sources will be acceptable as a first step, this approach is already prototyped at https://gitlab.com/BuildStream/buildstream/snippets/1731497.

If the implemented solution introduces non-determinism, it should be opt in with a new option on the git plugin, at least until a better solution can be achieved.