Add docs for bucket quota feature (#9503)

This PR also adds a check to not enforce
bucket quota for server-side metadata copy
of an object onto itself.

cmd/object-handlers.go

@@ -879,10 +879,12 @@ func (api objectAPIHandlers) CopyObjectHandler(w http.ResponseWriter, r *http.Re
 		}
 		length = actualSize
 	}
+	if !cpSrcDstSame {
 		if err := enforceBucketQuota(ctx, dstBucket, actualSize); err != nil {
 			writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL, guessIsBrowserReq(r))
 			return
 		}
+	}
 
 	var compressMetadata map[string]string
 	// No need to compress for remote etcd calls

docs/bucket/quota/README.md

@@ -0,0 +1,45 @@
+# Bucket Quota Configuration Quickstart Guide [![Slack](https://slack.min.io/slack?type=svg)](https://slack.min.io) [![Docker Pulls](https://img.shields.io/docker/pulls/minio/minio.svg?maxAge=604800)](https://hub.docker.com/r/minio/minio/)
+
+
+![quota](bucketquota.png)
+
+
+Buckets can be configured to have one of two types of quota configuration - FIFO and Hard quota.
+
+- `Hard` quota disallows writes to the bucket after configured quota limit is reached.
+
+- `FIFO` quota automatically deletes oldest content until bucket usage falls within configured limit while permitting writes.  
+
+## 1. Prerequisites
+- Install MinIO - [MinIO Quickstart Guide](https://docs.min.io/docs/minio-quickstart-guide).
+- [Use `mc` with MinIO Server](https://docs.min.io/docs/minio-client-quickstart-guide)
+
+
+
+## 2. Set bucket quota configuration
+
+1. Set a hard quota of 1GB for a bucket `mybucket` on MinIO
+object storage:
+
+```sh
+$ mc admin bucket quota myminio/mybucket --hard 1gb
+```
+
+2. Set FIFO quota of 5GB for a bucket "mybucket" on MinIO to allow automatic deletion of
+older content to ensure bucket usage remains within 5GB 
+
+```sh
+$ mc admin bucket quota myminio/mybucket --fifo 5gb
+```
+
+3. Verify the quota configured on `mybucket` on MinIO
+
+```sh
+$ mc admin bucket quota myminio/mybucket
+```
+
+4. Clear bucket quota configuration for `mybucket` on MinIO
+
+```sh
+$ mc admin bucket quota myminio/mybucket --clear
+```