Add Access Controls to Mongo

By default, Mongo comes with Access Controls disabled. We should enable them for the db container we provide in docker-compose. In a real production environment, users may be using something like MongoDB Atlas, or AWS's DocumentDB which would require some Access Control configuration on that end. In case users decide `docker-compose up` is just enough for their environment, we should provide some level of Access Control on the provided Mongo container for security and data integrity.

The current version of the db_seed.py script is really just for testing the database. We should probably rename that file to something like db_seed_dev.py and create a new db_seed.py file that would initialize the database with an account, a first user, and a database user that the application would use.

See this doc from Mongo for more information on Access Controls: https://docs.mongodb.com/manual/tutorial/enable-authentication/