Transfers ownership of an unattached storage volume to a target tenant.

This operation requires the caller to be a master-tenant user holding the
admin-accounts permission with Full access. Lacking this is the most common
cause of a 403 Access Denied.

The target tenant may be specified using any one of the equivalent fields
tenant.id, account.id, owner.id, or accountId. The tenant.id form is
the canonical/preferred representation.

Behavior and constraints:

• The volume must be unattached (status: "unattached" and not attached to any
  host or instance).
• The volume's backing datastore must be accessible to the target tenant.
• Transferring to the volume's current tenant is a no-op and returns success.

Related tenant-awareness changes apply to the storage volume list
(MORPH-12454) and get (MORPH-12455) endpoints.