reenable DEFAULT_LINUX_VERSION for cos7, alma8, alma9, etc.

[beckermr]

This option was removed when we dropped cos6.

Per the discussion on the core call, we are going to reenable this option since the CUDA zip in the pinnings makes it hard to do this in the cbc.yaml directly.

cc @h-vetinari @isuruf

[jakirkham]

Have implemented this for cos7 and alma8 in PR: #6548

It would be simple to extend to alma9 when we are ready

[h-vetinari]

I also updated my PR to do this (including the alma9 images and removing cdt_name from the zip). However, I wanted to note a pertinent comment in the discussion in #6548 that we could simply always use the newest available image by default. This should obsolete the necessity for DEFAULT_LINUX_VERSION completely, because the only point where we really need that is if we need a newer image for some reason.

This comment is mostly for cross-referencing purposes, I think the discussion fits better in #6283, which is where I put my thoughts on this.