Add docs for Azure Virtual Networks, Subnets, and Private Endpoints

[eerhardt]

See Add Support for Azure Virtual Networks and Private Endpoints (dotnet/aspire#13750) and dotnet/aspire#13108.

We are adding support for azure virtual networks, subnets, and private endpoints. We should document this new feature area.

[IEvangelist]

Is this intended for 13.2?

[eerhardt]

Is this intended for 13.2?

Yes, as preview / experimental.

[eerhardt]

Be sure to add a note about ServiceBus SKU - Fix Azure ServiceBus sku when using private endpoints (dotnet/aspire#14484)