Add new site replication feature (#13311)

This change allows a set of MinIO sites (clusters) to be configured 
for mutual replication of all buckets (including bucket policies, tags, 
object-lock configuration and bucket encryption), IAM policies, 
LDAP service accounts and LDAP STS accounts.

cmd/globals.go

@@ -256,6 +256,9 @@ var (
 	// Allocated etcd endpoint for config and bucket DNS.
 	globalEtcdClient *etcd.Client
 
+	// Cluster replication manager.
+	globalSiteReplicationSys SiteReplicationSys
+
 	// Is set to true when Bucket federation is requested
 	// and is 'true' when etcdConfig.PathPrefix is empty
 	globalBucketFederation bool