Allow resolving remote config dependencies from existing local clones

Currently Skaffold's `remote config dependencies` are downloaded into the `SKAFFOLD_REMOTE_CACHE_DIR` and any changes made there are reset on every run. It might be useful to be able to specify an already existing repo clone be used by skaffold to fulfil this dependency instead of using the one in the remote cache directory. Changes made in this clone would not be reset and it could be a handy way to test changes without always needing to push those changes upstream to the dependency git repo.

Discussed approach: Support a `local-repos-cache` flag that interprets a slice of strings as directories. For each directory in the specified order, Skaffold checks its git config or any git config in its immediate subdirectory that match the remote required by skaffold to fulfil a `remote config dependency`. Skaffold skips downloading found repos and uses the existing one instead(even with uncommitted changes, or a different branch).

cc. @briandealwis