Add support for sparse checkouts

[jonnelaaglandwinder]

I've taken a crack at implementing a sparse checkout option suggested in #172. It may prove useful for large monorepos, especially if a --filter option for fetch were to be implemented as well.

I've put a temporary escape hatch in the test script, since it would fail without the test data branch being present, but it should pass with those lines removed when the test data exists. (test-data/v2/sparse-checkout)

[arcanis]

Bump @thboop? This would be extremely useful for repositories that check-in (somewhat) large artifacts, like their zipped dependencies, which is a somewhat common pattern with Yarn.

[Wrathchyld]

action.yml

[tyson-benson]

This would be a great addition 👍 It would be a valuable capability for those that want to adopt mono-repo design. I hope this PR gets the attention it deserves.

[arcanis]

Ping @TingluoHuang? Are there any blockers?

[blu3mania]

Shouldn't lfs.fetchinclude also be set or use "-I" (or "--include") parameter in GitCommandManager.lfsFetch to make sure LFS only fetches from included paths?