virtiofsd live migration support

Creating this Epic to track the development of virtiofs live migration feature. Also will link various requests which have come from different sources to support this feature.

Acceptance Criteria

A list of specific needs or objectives must be delivered to satisfy the epic.

Required changes in QEMU:

• [ ] Internal migration support in QEMU
  https://listman.redhat.com/archives/virtio-fs/2023-April/005598.html

Required changes in rust-vmm crates:

• [x] Fix return value of GET_VRING_BASE message
  https://github.com/rust-vmm/vhost/pull/154

Required changes in virtiofsd:

• [x] Make Reader and Writer generic over bitmap
  https://gitlab.com/virtio-fs/virtiofsd/-/merge_requests/162

  What SSTs and Layered Product teams should review this?