Provide a decorator to indicate to the generator that service's response content stream should not be buffered

[annelo-msft]

Clear and concise description of the problem

In .NET Azure clients, we buffer response content by default in the client pipeline. This feature can be turned off for service methods that return a network stream to the end user. An example of this in a DPG client is shown here.

@m-nash has shared that TypeSpec does not currently provide a way to indicate to the generator that is should write a service method with response content buffering disabled. We have requested this feature from the generator here: Azure/autorest.csharp#4693

Checklist

• Follow our Code of Conduct
• Check that this issue is about the Azure libraries for typespec. For feature request in the typespec language or core libraries file it in the TypeSpec repo
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.