fbcode_builder: getdeps: fboss: add git-lfs fetcher
fbcode_builder: getdeps: fboss: add git-lfs fetcher

Summary:
As titled. This is needed by OpenBCM, and in future, possibly by other
manifests as well.

Reviewed By: wez

Differential Revision: D18759807

fbshipit-source-id: d445dfa382cea4bf96443ab9889926a4abbf0757

facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst