simplify webhook DNS further generalize for gateway (#10448)

continuation of the changes from eaaf05a7cc
this further simplifies, enables this for gateway deployments as well

cmd/config/dns/store.go

@@ -0,0 +1,28 @@
+/*
+ * MinIO Cloud Storage, (C) 2020 MinIO, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package dns
+
+// Store dns record store
+type Store interface {
+	Put(bucket string) error
+	Get(bucket string) ([]SrvRecord, error)
+	Delete(bucket string) error
+	List() (map[string][]SrvRecord, error)
+	DeleteRecord(record SrvRecord) error
+	Close() error
+	String() string
+}