use mongo version variable in docker-compose template - about to test upgrading from 4.0 to 4.2

templates/docker-compose.yml.j2

@@ -29,7 +29,7 @@ services:
       - "traefik.frontend.rule=Host: your.domain.tld"
 
   mongo:
-    image: mongo:4.0
+    image: mongo:{{ mongo_version }}
     restart: unless-stopped
     volumes:
       - ./data/db:/data/db
@@ -52,7 +52,7 @@ services:
       - ./data/db:/data/db
 
   mongo-init-replica:
-    image: mongo:4.0
+    image: mongo:{{ mongo_version }}
     command: >
       bash -c
         "for (( ; ; )); do