💪 [Enhance]: Mongo DB test fixtures to use the `.` separator instead of the forward slash `/`

Description

The Mongo DB separator is the dot . to separate between the Mongo DB database and collections. Because we use the forward slash / in the logging, it might seem confusing when this gets translated into real Azure resources during defect localization.

Solution

Use the dot . notation when logging Mongo DB collections in databases to streamline with the naming conventions of Mongo DB.

Additional context

Test fixtures are located in the Arcus.Testing.Storage.Cosmos project.