Ubuntu 20.04 is EOL, being removed from image server and Zabbly packages

Ubuntu 20.04 LTS public EOL was at the end of May.

We’ve begun the process of no longer building those images and also no longer publishing Incus packages for it.

I’m aware that Canonical provides various options for extended support, but all of those require some kind of subscription (often free) and it’s not something we can make use of on our builds or include within the images we’re building.