This is in an effort to simplify test automation around dependent diffs workflow.
If you have dependent diffs where some of the dependencies have already landed into HEAD, a arc patch --nobranch on the dependent diff fails since 'get cherry-pick' does not allow empty commits.
This lets you set a flag that gets passed down to git cherry-pick which allows and keeps empty commits around.

Fixes one of the problems mentioned in T5986

arc patch --nobranch D1 fails, but arc patch --nobranch --keep-redundant-commits D1 runs successfully and adds a empty commit to the working copy.