macos: packaging support for MacOS X 10.15

macos: packaging support for MacOS X 10.15

This commit introduces the new set of changes / files required to
successfully create the dmg installer on OS X 10.15 "Catalina".

Reviewed-on: https://gerrit.openafs.org/13669
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit c7864b73603842b8beaee03fcbb2426890205410)

Change-Id: I0b6b0616f2f2413a466c60986957e6bc3e21cbb0
Reviewed-on: https://gerrit.openafs.org/14034
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Yadavendra Yadav <yadayada@in.ibm.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>