The relevant bit is only one environment variable:
Everything else in that document you would need to to regardless, you need to create the DB, setup DB users to provide access to your DB, create the Galaxy application, deploy it, etc. That’s as simple as it gets really.
"MONGO_URL": "[YOUR MONGODB URI]"
While I appreciate that you may not be an IT guy, surely the person writing the Meteor application is?
Also, it’s not half of a service, it’s 100% of the service, they provide meteor application hosting, and not all Meteor apps use MongoDB, some use RethinkDB, some use Apollo now and interface with pretty much any data service. As such, if MDG did provide a MongoDB service, it would just add extra load on the servers for a service that may not even be needed.