Add API's for managing bucket quota (#9379)

This PR allows setting a "hard" or "fifo" quota
restriction at the bucket level. Buckets that
have reached the FIFO quota configured, will
automatically be cleaned up in FIFO manner until
bucket usage drops to configured quota.
If a bucket is configured with a "hard" quota
ceiling, all further writes are disallowed.

pkg/madmin/examples/bucket-quota.go

@@ -0,0 +1,56 @@
+// +build ignore
+
+/*
+ * 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 main
+
+import (
+	"context"
+	"fmt"
+	"log"
+
+	"github.com/minio/minio/pkg/madmin"
+)
+
+func main() {
+	// Note: YOUR-ACCESSKEYID, YOUR-SECRETACCESSKEY and my-bucketname are
+	// dummy values, please replace them with original values.
+
+	// API requests are secure (HTTPS) if secure=true and insecure (HTTP) otherwise.
+	// New returns an MinIO Admin client object.
+	madmClnt, err := madmin.New("your-minio.example.com:9000", "YOUR-ACCESSKEYID", "YOUR-SECRETACCESSKEY", true)
+	if err != nil {
+		log.Fatalln(err)
+	}
+	var kiB int64 = 1 << 10
+	ctx := context.Background()
+	// set bucket quota config
+	if err := madmClnt.SetBucketQuota(ctx, "bucket-name", 64*kiB, HardQuota); err != nil {
+		log.Fatalln(err)
+	}
+	// gets bucket quota config
+	quotaCfg, err := madmClnt.GetBucketQuota(ctx, "bucket-name")
+	if err != nil {
+		log.Fatalln(err)
+	}
+	fmt.Println(quotaCfg)
+	// remove bucket quota config
+	if err := madmClnt.RemoveBucketQuota(ctx, "bucket-name"); err != nil {
+		log.Fatalln(err)
+	}
+}