Horizon - Enabling migrate Cinder Volumes

Background:
Horizon dashboard do not have an option to enable the user to migrate Cinder volume from one backend to another, although the functionality is supported by Cinder CLI/API. This gap needs to be addressed.

Use Cases:
* Migrate volumes from one backend to another(of same backend type)

Proposal:
This proposal is to expose volume migrate functionality of Cinder in the volumes panel of the OpenStack dashboard (Project->Compute->Volumes and Admin->System Panel->Volumes). This would be a row action on the "volumes" in the volumes table. The backend supporting API would be Cinder-API and corresponding update to OpenStack Dashboard API needs to be done.