Implement Mongo Seeder

What does this MR do?

Adds a Mongo Seeder service.

• Populates User and Question DB if needed and shuts down.

Testing

• Ensure Docker's MongoDB instances have no documents in Users and Questions DBs.
• Run docker compose up --build.
• Login as with username 'a' and password 'a'.
• Question appears on page.

Relevant issues

Fixes missing seeding.

backend-services/feed-service/Dockerfile

@@ -16,9 +16,7 @@ RUN unzip -d svc target/universal/feed-service-1.0.0.zip \
     && rm svc/bin/*.bat \
     && mv svc/bin/* svc/bin/start
 
-# Delete the RUNNING_PID fle that incorrectly tells Play there is already an instance running
-RUN rm -f svc/RUNNING_PID
-
 EXPOSE 9000
 
-CMD svc/bin/start
+# Delete the RUNNING_PID fle that incorrectly tells Play there is already an instance running
+CMD rm -f svc/RUNNING_PID && svc/bin/start