Currenlty transfer service doesn't handle plain HTTP connection.
This commit fixes this issue by propagating
`(core/remotes/docker/config).HostOptions.DefaultScheme` from client to the
transfer service.
This commit also fixes ctr to use this feature for "--plain-http" flag.
Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>
4332794384