return the falback for diagnostic and send only diagnostic as multipart

Author: dudikeleti

tracer/src/Datadog.Trace/Debugger/Upload/DebuggerUploadApiBase.cs

@@ -5,6 +5,7 @@
 
 #nullable enable
 using System;
+using System.CodeDom;
 using System.Threading;
 using System.Threading.Tasks;
 using System.Web;
@@ -62,9 +63,9 @@ protected Task<IApiResponse> PostAsync(string uri, ArraySegment<byte> data)
         var request = _apiRequestFactory.Create(new Uri(uri));
         var isDebuggerV1 = uri.Contains(DebuggerV1Endpoint);
 
-        return isDebuggerV1
-                   ? request.PostAsync(data, MimeTypes.Json)
-                   : request.PostAsync([new("event", MimeTypes.Json, "event.json", data)]);
+        return this is DiagnosticsUploadApi && !isDebuggerV1
+                   ? request.PostAsync([new("event", MimeTypes.Json, "event.json", data)])
+                   : request.PostAsync(data, MimeTypes.Json);
     }
 
     private string GetDefaultTagsMergedWithGlobalTags()

tracer/src/Datadog.Trace/Debugger/Upload/DiagnosticsUploadApi.cs

@@ -25,7 +25,7 @@ private DiagnosticsUploadApi(
         {
             discoveryService.SubscribeToChanges(c =>
             {
-                Endpoint = c.DiagnosticsEndpoint;
+                Endpoint = c.DiagnosticsEndpoint ?? c.DebuggerEndpoint;
                 Log.Debug("DiagnosticsUploadApi: Updated endpoint to {Endpoint}", Endpoint);
             });
         }