Consider making certain snaps optional on ubuntu-classic installs

[jamesps-ebi]

We're evaluating the use of Ubuntu with TPM+FDE for workstation systems, but have found that certain snaps like firefox, snap-store, and firmware-updater cannot be removed because they are part of the model assertion.

In particular, the firmware-updater snap doesn't fully function on TPM+FDE systems anyway: https://bugs.launchpad.net/ubuntu/+source/fwupd/+bug/2065874

Attempting to remove it gives the following error:

error: cannot remove "firmware-updater": snap "firmware-updater" is not removable: snap is required

Arguably these apps are not essential to the running of the system, unlike pc-kernel. Do they need to be enforced always?