Add warning for plugin configs with unknown fields

Signed-off-by: Derek McGowan <derek@mcg.dev>

integration/build_local_containerd_helper_test.go

@@ -96,7 +96,7 @@ func buildLocalContainerdClient(t *testing.T, tmpDir string) *containerd.Client
 
 		// load the plugin specific configuration if it is provided
 		if p.Config != nil {
-			pc, err := config.Decode(p)
+			pc, err := config.Decode(ctx, p)
 			assert.NoError(t, err)
 
 			initContext.Config = pc