feat: Add container for MongoDb Atlas Local

[jeff-goddard]

Linked issue: #865

This adds a Mongo DB Atlas local container.

This works similarly to the Java container: https://java.testcontainers.org/modules/databases/mongodb/#mongodbatlaslocalcontainer

Like the java one, I added this into the same module as the normal Mongo container, but we can make it into its own module if this would be better.

Changes form standard mongo container:

1. Use different environment variables for configuration
2. Wait for the container healthcheck rather than the logs, as it takes a little longer for the search service to start.