[9.0]: Add docs on named configuration providers for resources

[captainsafia]

We're working on adding support for named configuration providers for Azure resources as described in https://github.com/dotnet/aspire/issues/5826.

We'll want to update the docs pages for each of the resource types to clarify that this named model is also possible. The initial set of supported values is included in this PR: https://github.com/dotnet/aspire/pull/5827