Add initial support for bucket lifecycle (#7563)

This PR is based off @sinhaashish's PR for object lifecycle
management, which includes support only for,
- Expiration of object
- Filter using object prefix (_not_ object tags)

N B the code for actual expiration of objects will be included in a
subsequent PR.

cmd/gateway-main.go

@@ -269,6 +269,9 @@ func StartGateway(ctx *cli.Context, gw Gateway) {
 	// Initialize policy system.
 	go globalPolicySys.Init(newObject)
 
+	// Create new lifecycle system
+	globalLifecycleSys = NewLifecycleSys()
+
 	// Create new notification system.
 	globalNotificationSys = NewNotificationSys(globalServerConfig, globalEndpoints)
 	if globalEtcdClient != nil && newObject.IsNotificationSupported() {