Register local content plugin from separate package

Update the local content plugin to register itself in a consistent way
as other plugins. This also allows the separate package to define its
own configuration more cleanly.

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

plugins/content/local/plugin/plugin.go

@@ -0,0 +1,37 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package plugin
+
+import (
+	"github.com/containerd/plugin"
+	"github.com/containerd/plugin/registry"
+
+	"github.com/containerd/containerd/v2/plugins"
+	"github.com/containerd/containerd/v2/plugins/content/local"
+)
+
+func init() {
+	registry.Register(&plugin.Registration{
+		Type: plugins.ContentPlugin,
+		ID:   "content",
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			root := ic.Properties[plugins.PropertyRootDir]
+			ic.Meta.Exports["root"] = root
+			return local.NewStore(root)
+		},
+	})
+}