feat(postgres): add split_postgres_connections filter and average pool fact

Compute POSTGRES_ALLOWED_AVG_CONNECTIONS once and propagate to app roles (gitlab, mastodon, listmonk, matrix, pretix, mobilizon, openproject, discourse). Fix docker-compose postgres command (-c flags split). Add unit tests. Minor env/locale tweaks and includes.

Conversation: https://chatgpt.com/share/68b48e72-cc28-800f-9c21-270cbc17d82a

roles/web-app-listmonk/tasks/main.yml

@@ -40,7 +40,7 @@
          "client_secret": OIDC.CLIENT.SECRET
       } | to_json }}
 
-- name: Update administrator email and password login in Listmonk
+- name: Update administrator email and password login in Listmonk (as superuser)
   shell: |
     docker exec -i {{ database_host }} psql \
       -U {{ database_username }} \