Update config migrations to decode using the plugin type

Ensure migration picks up defaults and correct ordering from the plugin
configuration. Ensures that the migration matches the behavior of the
default output and how the configuration will be loaded.

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

cmd/containerd/command/config.go

@@ -123,6 +123,28 @@ var configCommand = cli.Command{
 					}
 				}
 
+				plugins, err := server.LoadPlugins(ctx, config)
+				if err != nil {
+					return err
+				}
+				if len(plugins) != 0 {
+					if config.Plugins == nil {
+						config.Plugins = make(map[string]interface{})
+					}
+					for _, p := range plugins {
+						if p.Config == nil {
+							continue
+						}
+
+						pc, err := config.Decode(ctx, p.URI(), p.Config)
+						if err != nil {
+							return err
+						}
+
+						config.Plugins[p.URI()] = pc
+					}
+				}
+
 				config.Version = srvconfig.CurrentConfigVersion
 
 				return toml.NewEncoder(os.Stdout).SetIndentTables(true).Encode(config)