maas cannot provide all official maas images

Until 20.04, we had both i386 and x86_64 images for deployment from MAAS. Starting from 20.04, the i386 images were dropped.

HOWEVER, MAAS was never adjusted to compensate for this. When selecting images for download, you can only select the arch for ALL images, not specific images. Thus, because my MAAS servers are configured to download i386 images (they have been this way for as long as we've run MAAS) MAAS now throws an error every time it attempts to sync images because the i386 images do not exist at maas-images for 20.04.

SO MAAS needs to allow for per-release arch specifications. I've attached a screenshot to show the error.

To resolve this, MAAS should either ignore the missing 32bit images from now on, or should allow me to specify 32bit images for everything but 20.04 and later.