Draft: Update mount options

Hi, I'm opening this for discussion, because I'm wondering:

1. Can the fstab tab mount line generating script handle both the = and : symbols? Ie "compress=zstd:1" [Confirmed with local test. Well that was easy!]

2. How do I actually enable/preselect "nodiscard" by default?

3. Should we hide dangerous options like "nobarrier" by making them exclusive to expert mode? How?

4. The tooling around transparent compression is still horrible. It's still not possible to actually know how much free space you have, and running out of space with btrfs usually requires temporarily adding another device so that btrfs can create a workspace to do any required operation--including deleting files, snapshots, etc. Should this be hidden in expert mode?

This is the first half of partman-basicfilesystems!10

And the primary discussion is occurring here: https://lists.debian.org/debian-boot/2025/05/msg00229.html