Add multi-node block attach for live migration

[joeseegmiller]

Summary

This change adds support for multi-node block attach (RWX for block volumes) in the CSI driver, enabling compatibility with KubeVirt live migration.

Problem

The CSI driver did not support creating volumes for live migration scenarios that require multi-node block attach. As a result, those volumes could not be provisioned with the needed access mode.

Solution

Add support for MULTI_NODE_MULTI_WRITER for block volumes, and update controller and node validation to allow that access mode while continuing to reject it for mount volumes.

Testing

• Created multiple VMs using multi-node block volumes
• Verified successful live migration between nodes
• Tested concurrent attachment of the same volume across nodes
• Performed node drain and confirmed workloads remain available
• Stress-tested with multiple volumes per VM (20+)

Notes

Tested on OpenShift with KubeVirt using Dell ME5 storage backend.
MULTI_NODE_MULTI_WRITER is restricted to block volumes to align with CSI expectations and avoid unsafe shared filesystem usage.

[joeseegmiller]

I created this in response to my initial request in this issue:

#132

[jkeam]

This change looks pretty solid. Is there anyway we can get this merged in?