simply support environment variables expansion in database name or table name
this way a single configuration folder can be used to configure multiple realm apps
but each realm app will use a different database/table so the data is separated.
an official mongodb example code from a blog post about this topic uses this expansion but talking with support they said it is not supported and that the example code is wrong.

https://github.com/mongodb-developer/realm-demos/blob/main/inventory/export/sync/data_sources/mongodb-atlas/InventoryDemo/InventoryItem/rules.json