Previously, containerd uses Go's default UA "Go-http-client/1.1" while authenticating with registry.
This commit changes it to the pattern like "containerd/v1.5.2" which is used for all other requests.
Signed-off-by: Ethan Chen <pov@mahou-shoujo.moe>
This accomplishes a few long-standing TODO items, but also helps users
in showing exact registry error messages
Signed-off-by: Ilya Dmitrichenko <errordeveloper@gmail.com>