Describe the bug

Serverless: Deprecation warning: Variables resolver reports following resolution errors:
              - Cannot resolve variable at "provider.environment.CUBEJS_APP": Value not found at "self" source,
              - Cannot resolve variable at "functions.cubejsProcess.events.0.event.resource": Value not found at "self" source
            From a next major this will be

Currently, there is no authentication in our MongoDB tests.
Setting MONGO_INITDB_ROOT_USERNAME and MONGO_INITDB_ROOT_PASSWORD environment variables enable auth in MongoDB docker. https://hub.docker.com/_/mongo

1 issue description
2. fix bug, enhance....
3. git commit -m "issue name (#issue number)"

I am very curious about experience of newcomers with the tutorial. I am sure it can be improved to make onboarding easier.