Implement Progress Bar + Estimated Time Remaining + Cancel Button for Volume Snapshots

##### ISSUE TYPE

* Improvement Request

##### COMPONENT NAME

~~~
Volume Snapshots
~~~

##### CLOUDSTACK VERSION

~~~
4.19.0
~~~

##### CONFIGURATION

##### OS / ENVIRONMENT

##### SUMMARY

Currently when taking Volume Snapshots, users have no idea how long the operation takes.
Cloudstack will just show a circle loading animation, with no indication on progress or time left.
As a result, user does not know if there is a bug in the snapshot process, or its actually in progress.
This becomes even worse for large volumes (eg. 10TB) where it can take hours to complete.
And if the user waits too long, they will think the system hanged and would then attempt to create a new Volume Snapshot, resulting in 2 on going copies, which will slow down the entire system.

Volume Snapshot seems to be a very intensive operation. In this case, user should be allowed to cancel an ongoing volume snapshot if desired, to save system resources from an unmeaningful operation.

My suggestion is to add a progress bar to the following UI for better user experience:

This implementation should be neutral to the underlying storage, such as NFS, Object Storage, Ceph, Linstor etc

##### STEPS TO REPRODUCE

~~~

~~~

##### EXPECTED RESULTS

~~~
Better user experience for volume snapshots
~~~

##### ACTUAL RESULTS

~~~
- Cant tell if Volume Snapshot hanged, or is in progress (especially large Volumes)
- Cant monitor progress of snapshot
- Cant cancel Volume Snapshot
~~~

先檢視連結的螢幕截圖中顯示的 Volume Snapshots UI，以及現有的 snapshot 操作流程。定義進度、預估時間和取消在 NFS、Object Storage、Ceph 與 Linstor 上應如何運作；完成表示使用者可以監控和取消 snapshot，而不需要儲存體特定的行為。

由索引模型根據 Issue 內容生成。