Upgrade Refstack's MariaDB to 10.11

We are currently running MariaDB 10.4 for refstack. We use the
MARIADB_AUTO_UPGRADE flag to automatically upgrade the mariadb install
to 10.11 when switching the image version over to 10.11. This was
successfully performed against the lodgeit paste service.

Change-Id: I75262bc8eba3dd59d5869be9bf568fd66dc7f608

playbooks/roles/refstack/templates/docker-compose.yaml.j2

@@ -4,7 +4,7 @@ version: '2'
 
 services:
   mariadb:
-    image: docker.io/library/mariadb:10.4
+    image: docker.io/library/mariadb:10.11
     network_mode: host
     restart: always
     environment:
@@ -12,6 +12,7 @@ services:
       MYSQL_DATABASE: refstack
       MYSQL_USER: "{{ refstack_db_username }}"
       MYSQL_PASSWORD: "{{ refstack_db_password }}"
+      MARIADB_AUTO_UPGRADE: 1
     volumes:
       - /var/lib/refstack/db:/var/lib/mysql
     logging: