- printing role: Add configurable printerName, printerUri, and printerModel options
to replace hardcoded Brother printer values
- nfs-mounts role: Add configurable server, remotePath, and mountPoint options
to replace hardcoded NFS server IP (10.0.0.43)
- virtualisation role: Add configurable dockerUsers option as list type
to replace hardcoded 'johno' docker group membership
All options have sensible defaults matching the original hardcoded values,
ensuring backward compatibility while allowing per-host customization.
Implements bead: nixos-configs-fkt
