Feature request: git submodule context about metadata-action

[crazy-max]

I think we could add a separator to the git context following by the path you want to use. Something like:

      -
        name: Docker meta
        id: meta
        uses: docker/metadata-action@v4
        with:
          context: "git:foo"

Where foo is a submodule.

But then GitHub metadata attached to the Git context would be quite wrong imo so I'm not sure.