Add a CI check to prevent unwanted bloat in binary images,
by building a baseline (pre-PR) binary then comparing file
sizes post-PR.
Part 1 (#13518) added a new script that runs multiple 'make's,
comparing image sizes against an original, and failing loudly
if growth is too big. An override mechanism is defined.
This is part 2 of 2: adding the CI rule. We couldn't do that
in part 1, because the rule would call a script that didn't
exist in the pre-PR commit.
Signed-off-by: Ed Santiago <santiago@redhat.com>