Move client to subpackage

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

client/export.go

@@ -0,0 +1,31 @@
+/*
+   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 client
+
+import (
+	"context"
+	"io"
+
+	"github.com/containerd/containerd/v2/images/archive"
+)
+
+// Export exports images to a Tar stream.
+// The tar archive is in OCI format with a Docker compatible manifest
+// when a single target platform is given.
+func (c *Client) Export(ctx context.Context, w io.Writer, opts ...archive.ExportOpt) error {
+	return archive.Export(ctx, c.ContentStore(), w, opts...)
+}