git: option to exclude deleted files

[andheiberg-babylonhealth]

I'm using this as a CI step to require explicit owners for a monolith owned by multiple teams. Currently the CI step will fail if someone deletes a file that didn't have an explicit owner. This is obviously not desirable.

It would be nice to have an option like:

github-codeowners git --exclude-deleted-files develop HEAD

This way the CI can enforce that all new or modified files have owners.