Provide a way to indicate that a parameter is a "client parameter"

[annelo-msft]

We would like a way to indicate that the hub parameter in WebPubSub is a "client parameter", meaning it is a private member on the client and taken as a parameter to the client constructor (see WebPubSub APIView).

In swagger, this could be indicated as a global parameter, or by using the x-ms-parameter-location extension and setting the value to client.

[lmazuel]

Do-able short term with:

import "@cadl-lang/openapi";

@doc("The mode with which you'll be handling your returned body. 'raw' for just dealing with the raw body, and 'model' if you are going to convert the raw body to a customized body before returning to users.")
model ModeParameter {
  @OpenAPI.extension("x-ms-parameter-location", "method")
  @doc("The mode with which you'll be handling your returned body. 'raw' for just dealing with the raw body, and 'model' if you are going to convert the raw body to a customized body before returning to users.")
  @path
  mode: Mode;
}

But agree we need a design that don't use OpenAPI.extension long term.

It does generate the right OpenAPIv3, which autorest no problem to consume.

[markcowl]

Discuss with #656

[daviwil]

Implementation issue: #778