Aggregator: Add mutation and validation handlers (#92036)

pkg/aggregator/apiserver/plugin/fakes/http.go

@@ -0,0 +1,13 @@
+package fakes
+
+import "net/http"
+
+func NewFakeHTTPHandler(status int, res []byte) http.HandlerFunc {
+	return func(w http.ResponseWriter, req *http.Request) {
+		w.WriteHeader(status)
+		_, err := w.Write(res)
+		if err != nil {
+			panic(err)
+		}
+	}
+}