Upload hook that guides people towards AOSP.

The canonical location of certain parts of the source tree live in
AOSP, and should not be changed internally to avoid merge conflicts.

This initially starts with "OWNERS" files, but the hook can easily
be repeated to match any files based on file path regexes.

Bug: 113136846
Test: manual
Change-Id: I113e63b6133f20389d84ec0d6d8b81cdbdf35d38