feat: Set up filesystems

Automatically set up btrfs root and data filesystem, as well as external
HDD.

This automation change assumes a layout exactly as in current bob to
function by default, can be changed to any btrfs layout with the
`btrfs_mounts` configuration option, however.

site.yaml

@@ -20,6 +20,11 @@
 - name: Prepare incus server host
   hosts: host_system
   tasks:
+    - name: Prepare host filesystems
+      ansible.builtin.import_role:
+        name: filesystem
+      tags: filesystem
+
     - name: Prepare system
       ansible.builtin.import_role:
         name: system