migration: Convert the file backend to the new QAPI syntax

Convert the file: URI to accept a FileMigrationArgs to be compatible
with the new migration QAPI.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <20231023182053.8711-9-farosas@suse.de>
3 files changed