Upgrade minimum version of MongoDB required for the adaptor (#1061)

Author: Adrian Clay

OPERATING.md

@@ -28,7 +28,10 @@ You can provide an external `logback.xml` file using the `-Dlogback.configuratio
 
 ### Database Configuration Options
 
-The adaptor requires a Mongodb-compatible database to manage its internal state.
+The adaptor requires a Mongodb-compatible database of at least version 4.0 to manage its internal state.
+MongoDB provides [a table of compatible versions of their product against the java driver version][mongodb-compatible-versions].
+
+[mongodb-compatible-versions]: https://www.mongodb.com/docs/drivers/java/sync/current/compatibility/#compatibility-table-legend
 
 | Environment Variable            | Default                   | Description                                                                                                                                                    |
 |---------------------------------|---------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------|

docker/docker-compose.yml

@@ -60,9 +60,9 @@ services:
       - GP2GP_AMQP_MAX_REDELIVERIES
 
   mongodb:
-    networks: 
+    networks:
       - commonforgp2gp
-    image: mongo:3.6.23
+    image: mongo:4.0.28
     ports:
       - "27017:27017"