add postgres support mx-appservice-[slack|irc] with fallback to nedb in role and migration notice

roles/matrix-bridge-appservice-slack/templates/config.yaml.j2

@@ -9,9 +9,11 @@ homeserver:
     url: "{{ matrix_appservice_slack_homeserver_url }}"
     server_name: "{{ matrix_domain }}"
 
+{% if matrix_appservice_slack_database_engine == 'nedb' %}
 dbdir: "/data"
+{% endif %}
 db:
-    engine: "postgres"
-    connectionString: "postgresql://matrix_appservice_slack:{{ matrix_addtional_databases | selectattr('name', 'equalto', 'matrix_appservice_slack') | map(attribute='pass') | first }}@{{ matrix_postgres_connection_hostname }}/matrix_appservice_slack"
+    engine: "{{ matrix_appservice_slack_database_engine }}"
+    connectionString: {{ matrix_appservice_slack_database_connString | to_json }}
 
 matrix_admin_room: "{{ matrix_appservice_slack_control_room_id }}"