manatee: Add schema

The household weekly plan at schema.ppp.pm: its module, certificate,
DNS record, backup and secrets. The link to puppy-tracker is prepared
but commented out until puppy-tracker with the integration feed is
deployed.

hosts/manatee/modules/restic/default.nix

@@ -104,6 +104,7 @@ let
     snapshot /var/lib/puppy-tracker        "$STATE/puppy-tracker"
     snapshot /var/lib/solo-referee         "$STATE/solo-referee"
     snapshot /var/lib/todo                 "$STATE/todo"
+    snapshot /var/lib/schema               "$STATE/schema"
     snapshot /var/lib/komga-book-manager   "$STATE/komga-book-manager"
     snapshot /var/lib/komga-reading-stats  "$STATE/komga-reading-stats"