add retryafter header (#38875)

Co-authored-by: Pan Shao <97225342+pshao25@users.noreply.github.com>

Author: mcgallan

specification/newrelic/NewRelicObservability.Management/NewRelicMonitorResource.tsp

@@ -112,7 +112,8 @@ interface NewRelicMonitorResources {
   switchBilling is ArmResourceActionSync<
     NewRelicMonitorResource,
     SwitchBillingRequest,
-    ArmResponse<NewRelicMonitorResource> | AcceptedResponse | NoContentResponse
+    ArmResponse<NewRelicMonitorResource> | (AcceptedResponse &
+      Azure.Core.Foundations.RetryAfterHeader) | NoContentResponse
   >;
 
   /**

specification/newrelic/resource-manager/NewRelic.Observability/preview/2025-05-01-preview/NewRelic.json

@@ -1786,7 +1786,14 @@
             }
           },
           "202": {
-            "description": "The request has been accepted for processing, but processing has not yet completed."
+            "description": "Azure operation completed successfully.",
+            "headers": {
+              "Retry-After": {
+                "type": "integer",
+                "format": "int32",
+                "description": "The Retry-After header can indicate how long the client should wait before polling the operation status."
+              }
+            }
           },
           "204": {
             "description": "There is no content to send for this request, but the headers may be useful."