In order to reduce the load on our builder nodes and reduce the strain
on our providers' image stores, build most images only once per week.
Exceptions are ubuntu-jammy, our most often used distro image, which we
keep rebuilding daily, and some other more frequently used images built
every 2 days.
Change-Id: Ibba7f864b15e478fda59c998843c3b2ace0022d8
d0c0ddb977