feat(git-clone): add ability to recurse submodules

I'm currently writing a Coder template for a project that needs submodules to be cloned.

With the git CLI you'd use `git clone --recurse-submodules` but there's no such option with the current module.
I think a `recurse_submodule = true` variable would be adequate.

If I get the time, I will submit a PR :-)