Add basic bandwidth monitoring for replication. (#10501)

This change tracks bandwidth for a bucket and object

- [x] Add Admin API
- [x] Add Peer API
- [x] Add BW throttling
- [x] Admin APIs to set replication limit
- [x] Admin APIs for fetch bandwidth

pkg/bandwidth/bandwidth.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 bandwidth
+
+// Details for the measured bandwidth
+type Details struct {
+	LimitInBytesPerSecond            int64   `json:"limitInBits"`
+	CurrentBandwidthInBytesPerSecond float64 `json:"currentBandwidth"`
+}
+
+// Report captures the details for all buckets.
+type Report struct {
+	BucketStats map[string]Details `json:"bucketStats,omitempty"`
+}