Add coverage for custom LRO RPC

[catalinaperalta]

We should have coverage for LRO RPC operations that follow a similar format to what Health Insights supports.

Link to the TypeSpec: link

Custom LRO RPC template:

@doc("Long running RPC operation template")
@post
op TLongRunningRpcOperation<
  TParams,
  TResponse
> is Azure.Core.Foundations.Operation<
  TParams & RepeatabilityRequestHeaders,
  (Foundations.AcceptedResponse<Foundations.LongRunningStatusLocation<TResponse> &
    Foundations.RetryAfterHeader> &
    RepeatabilityResponseHeaders),
  RepeatabilityRequestHeaders & RepeatabilityResponseHeaders,
  Azure.Core.Foundations.ErrorResponse
>;

Link to operation defintion: link

LRO RPC template usage:

op createJob is TLongRunningRpcOperation<OncoPhenotypeData, OncoPhenotypeResult>;

Health Insights LRO behavior:

1. Initial POST request to the service with input data in OncoPhenotypeData.
2. 202 response returned with Operation-Location header, as well as repeatability and retry headers, no body.
3. Poll at Operation-Location url.
4. Receive 200 response with final payload OncoPhenotypeResult.

[weidongxu-microsoft]

We've had it here #342
But it is not fully reviewed by Mark. We are waiting for issue https://github.com/Azure/typespec-azure/issues/3108 (seems re-routed to Aug)

The template in cadl-ranch lro/rpc/legacy mostly reflect the runtime behavior, except the | TResponse in the last line of

    Foundations.AcceptedResponse<{
      @pollingLocation
      @doc("The location for monitoring the operation state.")
      @TypeSpec.Http.header("Operation-Location")
      operationLocation: TypeSpec.Rest.ResourceLocation<TPollResponse>;
    } & Foundations.RetryAfterHeader> | TResponse

It kind of follow a traditional solution in Swagger, that adding an additional 200 with the "logical result" or "final result" schema. But service never return 200 in that POST.

Removing the | TResponse would cause problem (as "logical result" from helper be empty model; I'd assume the schema of 202 get used instead). This would need to be double checked with Mark on helper method, if we really want to do this.

---

PS: Mike had a "final-state-schema" in Swagger that will get rid of the extra 200.
https://github.com/Azure/autorest/blob/main/docs/extensions/readme.md#x-ms-long-running-operation-options

But it may take time to get adopted.