fix: Install with recommends when installing grub/shim packages in arm ubuntu-cpc minimized images (LP: #2037075)
With the migration from linux-kvm to linux-virtual/genreic for the mantic minimal
images we can now start building arm64 minimal cloud images.
When building initial test images we noticed that when comparing the amd64 minimized images
and the arm64 images that the efibootmgr package was not installed in the arm64 images.
This is because for amd64 it is installed as a recommends of shim-signed but for arm64
we are installing shim-signed `--no-install-recommends`.
This commit ensures that we align more with amd64 install of grub/shim packages for arm
images and also install recommends packages.
For arm64 this ensures that efibootmgr is installed too.
fix: install LXD snap from stable/ubuntu-<version> channel (LP: #2036725)
In the past, we'd directly snap install lxd which defaults to
the latest/stable channel. However, whilst working on enhancing
unminimize, it was observed that we install this snap from
the stable/ubuntu-<version> channel instead.
This was also noted as a failure when running the CTF tests:
`lxd installed from latest/stable, not stable/ubuntu-23.10`
