Move plugin type definitions to containerd plugins package

The plugins packages defines the plugins used by containerd.
Move all the types and properties to this package.

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

services/tasks/local_freebsd.go

@@ -18,11 +18,12 @@ package tasks
 
 import (
 	"github.com/containerd/containerd/plugin"
+	"github.com/containerd/containerd/plugins"
 )
 
 var tasksServiceRequires = []plugin.Type{
-	plugin.EventPlugin,
-	plugin.RuntimePluginV2,
-	plugin.MetadataPlugin,
-	plugin.TaskMonitorPlugin,
+	plugins.EventPlugin,
+	plugins.RuntimePluginV2,
+	plugins.MetadataPlugin,
+	plugins.TaskMonitorPlugin,
 }