Volume Retype

This will enable a user to change a volume's type after its creation. This is useful for changing QoS settings (e.g., a volume that sees heavy usage once a month), changing properties (e.g., compressed/uncompressed), etc.

Migrating the volume will be necessary if:
1. The volume's current host cannot handle the new type
2. The volume's driver cannot change the type

In either case, migration will be policy-based, where the policy is passed via scheduler hints. The options are:
1. Never migrate
2. Migrate if necessary (default)
3. Migrate if necessary using host-based copy

This blueprint does not cover QoS and encryption, which require special handling.