bug#59972: confusing behavior when sshfs mount enabled

[Jeremiah]

If one adds the following to their guix configuration:

(file-system
    (mount-point "/srv/share")
    (device "username@server:/mountpoint/")
    (type "fuse.sshfs")
    ;; sshfs can't be set to #t or you'll get a weird error and no explaination
    ;; So that is a lovely bug in guix
    (mount? #f)
    (options "noauto,users,allow_other,IdentityFile=/root/.ssh/credential"))

and changes mount? to #t guix reconfigure will fail with a hard to
understand debug trace.

So either guix needs to make a meaningful error message or fix why it
currently doesn't allow sshfs filesystems to automount on boot

-Jeremiah