Build and sign distros provisioning issues

[brooksn]

Some images that are synced to the prime registry as part of the KDM release should be built independently for the prime registry.

Pre-release versions using prime assets or for prime-only versions should be pushed to the staging registry.

To test, a pre-release version should be tagged for one current version of k3s and for one current version of rke2. It should be verified that those images are pushed to the staging registry, in addition to docker hub.

These are the affected images:

• system-agent-installer-rke2
• system-agent-installer-k3s
• rke2-upgrade
• k3s-upgrade