Collapse our 2 MongoDB services into 1

[am-MongoDB]

Is your feature request related to a problem? Please describe.
We currently have two MongoDB services in the Realm app - one for sync, and one for everything else. It appears that the Realm UI now allows you to have a single MongoDB service that has sync enabled and also allows you to define rules for apps to access the Atlas data. We should (if possible) replace our two MongoDB services with a single one.

Describe the solution you'd like
Use a single MongoDB service for both Realm Sync and direct application access.

Additional context
When the app was written, you couldn't add both sync and rules to a single MongoDB service.

[o-fish-wildaid]

Raise new issues resulting from using/testing the apps