[Azure Functions] Skip instrumenting orchestrator functions (#7640)

## Summary of changes

`[PreserveContext]` on
`Microsoft.Azure.Functions.Worker.Pipeline.FunctionExecutionMiddleware.Invoke`
to force `ConfigureAwait(continueOnCapturedContext: true)` on returned
tasks

## Reason for change

Orchestrator functions have special constraints:
https://learn.microsoft.com/en-us/azure/azure-functions/durable/durable-functions-code-constraints?tabs=csharp#orchestrator-code-constraints

We are currently breaking applications for users of Azure durable
functions, as we are interferring with the determinism of the
orchestrator functions by wrapping the returned tasks and continuing in
a different context.

Author: pablomartinezbernardo

tracer/src/Datadog.Trace/ClrProfiler/AutoInstrumentation/Azure/Functions/Isolated/FunctionExecutionMiddlewareInvokeIntegration.cs

@@ -42,6 +42,7 @@ internal static CallTargetState OnMethodBegin<TTarget, TFunctionContext>(TTarget
     /// <param name="exception">Exception instance in case the original code threw an exception.</param>
     /// <param name="state">Calltarget state value</param>
     /// <returns>A response value, in an async scenario will be T of Task of T</returns>
+    [PreserveContext]
     internal static TReturn OnAsyncMethodEnd<TTarget, TReturn>(TTarget instance, TReturn returnValue, Exception exception, in CallTargetState state)
     {
         state.Scope?.DisposeWithException(exception);