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

[phorcys420]

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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 :-)

[michaelbrewer]

Probably also good to expose --jobs=<n> flag to speed up cloning submodules.