Safety guard: Make sure that we have at least shim & grub packages as part of the update #994
Description
In the future we will likely want to be generic, but as a safety check for now, let's make sure that we have at least shim and grub as part of the update payload on x86_64 & aarch64 at least.
We should fail at image build time (generate metadata), not at deploy time.
This is to prevent a future instance of: fedora-silverblue/issue-tracker#671