postgresql/default-cluster: Add Home Assistant DB

I actually created this a long time ago, but forgot to update the
manifest in Git.

The *homeassistant* database is used by Home Assistant for its
*recorder* component, which stores long-term statistics.  The data
stored here are only used for e.g. History and Logbook; current entity
states are still stored on the filesystem.

postgresql/default-cluster.yaml

@@ -16,6 +16,9 @@ spec:
     - createdb
     firefly-iii.firefly:
     - login
+    home-assistant.homeassistant:
+    - login
   databases:
     dustin: dustin
     firefly: firefly-iii.firefly
+    homeassistant: home-assistant.homeassistant