The user can define the setting `git.private-commits` as they desire. For
example:
git.private-commits = 'description(glob:"wip:*")'
If any commits are in this revset, then the push is aborted.
If a commit would be private but already exists on the remote, then it does
not block pushes, nor do its descendents block pushes unless they are also
contained in `git.private-commits`.
Closes#3376