CI: add periodic-stable-jobs Zuul project template

Kolla has it already and kolla-ansible should.
Patch to backport as far as pike.
Affects only stable branches.

Change-Id: Iecc46b364ad9fc69fe67dd09ee1b4e3c5511f01c
Signed-off-by: Radosław Piliszek <radoslaw.piliszek@gmail.com>