Idea: In git-fetcher, use shallow clone instead of full clone

[kenrick95]

In a monorepo where lots of dependencies are pointing to git repo, PNPM may still feel slow when it's fetching git contents. From the codes in packages/git-fetcher/src/index.ts, I guess each git dependency is still fully cloned, which may be slow if those git dependency is a huge repo.

Since we already resolved the commit to check out, I'm wondering if it is feasible to only fetch that specific commit only? Reference: https://stackoverflow.com/questions/61539881/git-shallow-clone-several-specific-refs-commits-which-are-not-branches

Thanks~

[kenrick95]

solved here: #4548