changed default postgres logic and optimized discourse postgres integration

roles/docker-discourse/templates/app.yml.j2

@@ -8,7 +8,9 @@
 ## visit http://www.yamllint.com/ to validate this file as needed
 
 templates:
+{% if enable_central_database | bool %}
   - "templates/postgres.template.yml"
+{% endif %}
   - "templates/redis.template.yml"
   - "templates/web.template.yml"
   ## Uncomment the next line to enable the IPv6 listener

roles/docker-discourse/vars/main.yml

@@ -1,4 +1,3 @@
 docker_compose_project_name:        "discourse"
 database_password:                  "{{ baserow_database_password }}"
-database_version:                   "{{ baserow_database_version | default(postgres_default_version) }}"
 database_type:                      "postgres"