Add docs for CosmosDB vnext-preview emulator

[eerhardt]

Describe the issue or suggestion

See Add support for CosmosDB vnext-preview emulator (dotnet/aspire#7048)

We added 2 new methods:

• RunAsPreviewEmulator
• WithDataExplorer

We should add those to our docs and explain how to use the new CosmosDB emulator with Aspire, and link to the CosmosDB docs on it.

[eerhardt]

cc @IEvangelist

[eerhardt]

Since these APIs are experimental, we should also ensure https://learn.microsoft.com/en-us/dotnet/aspire/diagnostics/overview is updated with the new diagnostics ID.

[eerhardt]

Note the diagnostics ID was recently renamed to ASPIRECOSMOSDB001