[Sample/Documentation] Sample for Cosmos RBAC

To me the documentation around cosmos RBAC doesnt contain nearly enough samples for ARM, let alone Bicep, so it would be great if someone would create samples around it:

https://docs.microsoft.com/en-us/azure/cosmos-db/how-to-setup-rbac

Start with the linked Azure Cosmos DB RBAC documentation and identify which ARM and Bicep sample scenarios are missing. Done means the requested Cosmos RBAC scenarios are documented with samples for both ARM and Bicep, with the examples consistent with the linked setup guide.

Written by the indexing model from the issue text.