Use uupd for updates

[castrojo]

Let's use https://github.com/ublue-os/uupd for the updates.

• We need to smoke test it for the other images anyway
• It'll be easier/cleaner to not bring all those old service units here for flatpak, brew, rpm-ostree, etc.

[tulilirockz]

ublue-os/uupd#42 should be literally the last step to adding this. The RPM seems to build fine, everything looks good, we can just create a COPR and add it here and BAM, done for testing

[gerblesh]

All merged if you want to start trying it out, released under a "prerelease" but once I get around to testing it I'll probably make an official v1.0 release