Add storage roadmap for ks 3.0

Signed-off-by: NXin Wang <wileywang@yunify.com>

docs/roadmap.md

@@ -28,6 +28,13 @@ KubeSphere Roadmap demonstrates a list of open source product development plans
 
 #### Multi-cluster
 
+- [ ] Snapshot management
+- [ ] Volume cloning
+- [ ] Volume monitoring and alerting
+- [ ] Identify storage system capabilities
+- [ ] Restore volume to available status
+- [ ] Unified integrate third-party storage plugin
+
 #### DevOps
 
 #### Observability