Fixes duplicating response headers in RateLimitingPlugin (#348)

Author: waldekmastykarz

m365-developer-proxy-plugins/Behavior/RateLimitingPlugin.cs

@@ -119,7 +119,15 @@ private void UpdateProxyResponse(ProxyHttpEventArgsBase e, HttpStatusCode errorS
         }
 
         // add headers to the original API response
-        e.Session.HttpClient.Response.Headers.AddHeaders(headers);
+        headers.ForEach(h => {
+            if (!response.Headers.HeaderExists(h.Name)) {
+                e.Session.HttpClient.Response.Headers.AddHeader(h);
+            }
+            else {
+                e.Session.HttpClient.Response.Headers.RemoveHeader(h.Name);
+                e.Session.HttpClient.Response.Headers.AddHeader(h);
+            }
+        });
     }
     private static string BuildApiErrorMessage(Request r) => $"Some error was generated by the proxy. {(ProxyUtils.IsGraphRequest(r) ? ProxyUtils.IsSdkRequest(r) ? "" : String.Join(' ', MessageUtils.BuildUseSdkForErrorsMessage(r)) : "")}";