UPSTREAM: <carry>: add shutdown annotation to response header

If it is useful we will combine this with the following carry:
20caad9: UPSTREAM: 115328: annotate early and late requests

staging/src/k8s.io/apiserver/pkg/server/filters/with_early_late_annotations.go

@@ -119,10 +119,11 @@ func withShutdownLateAnnotation(handler http.Handler, shutdownInitiated lifecycl
 			self = fmt.Sprintf("%s%t", self, requestor.GetName() == user.APIServerUser)
 		}
 
-		audit.AddAuditAnnotation(req.Context(), "apiserver.k8s.io/shutdown",
-			fmt.Sprintf("%s %s loopback=%t", late, self, isLoopback(req.RemoteAddr)))
+		message := fmt.Sprintf("%s %s loopback=%t", late, self, isLoopback(req.RemoteAddr))
+		audit.AddAuditAnnotation(req.Context(), "apiserver.k8s.io/shutdown", message)
 
 		handler.ServeHTTP(w, req)
+		w.Header().Set("X-OpenShift-Shutdown", message)
 	})
 }
 

staging/src/k8s.io/apiserver/pkg/server/filters/with_early_late_annotations_test.go

@@ -230,6 +230,9 @@ func TestWithShutdownLateAnnotation(t *testing.T) {
 					t.Logf("got: %s", valueGot)
 					t.Errorf("expected annotation to match, diff: %s", cmp.Diff(test.annotationShouldContain, valueGot))
 				}
+				if header := w.Header().Get("X-OpenShift-Shutdown"); !strings.Contains(header, test.annotationShouldContain) {
+					t.Errorf("expected response header to match, diff: %s", cmp.Diff(test.annotationShouldContain, header))
+				}
 			}
 		})
 	}