Explain the split in RabbitMQ and MongoDB client integration packages

[eerhardt]

Describe the issue or suggestion

RabbitMQ and MongoDB libraries recently made major breaking changes to their client libraries.

See

• RabbitMQ.Client v7 breaks Aspire.RabbitMQ.Client component (dotnet/aspire#3956)
• MongoDB.Driver v3 breaks Aspire.MongoDB.Driver integration (dotnet/aspire#6380)

We have split our client integrations into 2 - one for each side of the major breaking changes. So customers can pick which version they want to consume.

We should explain why there are 2 packages and how to pick which to use.