Improve performance for git dependencies

[beeb]

At the moment, the git dependencies download method performs the following:

• Clone entire repository (not recursive, no submodules)
• Git checkout to the desired rev if any
• Git rev-parse HEAD to get the checked out commit hash

If submodules are not desired, then we could maybe instead do

• a shallow clone (when no "rev" is present), but then checkout and rev-parse will not work
  • e.g. for the chainlink repo, normal cloning takes 32 seconds, shallow takes 5 seconds
• a tree-less clone (with --filter=tree:0), which is faster and pulls trees as needed (so checkout and rev-parse work)
  • e.g. for the chainlink repo, tree-less takes 10 seconds
• hitting the zip file instead (at https://github.com/owner/repo/archive/[commit].zip)

[beeb]

Working on it, for now I added --filter=tree:0 which seems to be the less disturbing solution.

[mario-eth]

We need to make sure it will work with tags and branches and everything that we added new