avoid double pushing with docker driver with containerd

In this mode buildkit can push directly so pushing manually
with docker would result in pushing image twice.

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

driver/docker/driver.go

@@ -93,6 +93,7 @@ func (d *Driver) Features(ctx context.Context) map[driver.Feature]bool {
 			driver.DockerExporter: useContainerdSnapshotter,
 			driver.CacheExport:    useContainerdSnapshotter,
 			driver.MultiPlatform:  useContainerdSnapshotter,
+			driver.DirectPush:     useContainerdSnapshotter,
 			driver.DefaultLoad:    true,
 		}
 	})