fix: add redis as a service dependency for the course-discovery service (#1040)

The Discovery service uses redis but it is not currently listed as a service dependency in our `docker-compose.yml` file. This results in errors when adding/updating/removing data in Devstack's version of Discovery (e.g. adding a new organization).

Author: justinhynes

docker-compose.yml

@@ -336,6 +336,7 @@ services:
       - memcached
       - mysql57
       - opensearch12
+      - redis
     # Allows attachment to the discovery service using 'docker attach <containerID>'.
     stdin_open: true
     tty: true