Pass snapshotter opts during Pull

For remote snapshotter cases it's quite often there is need to pass extra info
from client (for instance - registry URL to query remote layer from, credentials, etc).

This commit slightly extends WithPullSnapshotter to pass extra labels to a snapshotter.

Signed-off-by: Maksym Pavlenko <makpav@amazon.com>

pull.go

@@ -72,7 +72,7 @@ func (c *Client) Pull(ctx context.Context, ref string, opts ...RemoteOpt) (_ Ima
 		if err != nil {
 			return nil, errors.Wrap(err, "create unpacker")
 		}
-		unpackWrapper, unpackEg = u.handlerWrapper(ctx, &unpacks)
+		unpackWrapper, unpackEg = u.handlerWrapper(ctx, pullCtx, &unpacks)
 		defer func() {
 			if err := unpackEg.Wait(); err != nil {
 				if retErr == nil {