shim: Move ttrpc interceptors to plugins

This makes it so we don't need to import otelttrpc unless the shim is
compiled with the `shim_tracing` build tag.
This way otel is no longer compiled into the binary at all unless
`shim_tracing` is set.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

pkg/tracing/plugin/ttrpc.go

@@ -0,0 +1,47 @@
+/*
+   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/containerd/v2/plugins"
+	"github.com/containerd/otelttrpc"
+	"github.com/containerd/plugin"
+	"github.com/containerd/plugin/registry"
+	"github.com/containerd/ttrpc"
+)
+
+func init() {
+	const pluginName = "otelttrpc"
+
+	registry.Register(&plugin.Registration{
+		ID:   pluginName,
+		Type: plugins.TTRPCPlugin,
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			return otelttrpcopts{}, nil
+		},
+	})
+}
+
+type otelttrpcopts struct{}
+
+func (otelttrpcopts) UnaryServerInterceptor() ttrpc.UnaryServerInterceptor {
+	return otelttrpc.UnaryServerInterceptor()
+}
+
+func (otelttrpcopts) UnaryClientInterceptor() ttrpc.UnaryClientInterceptor {
+	return otelttrpc.UnaryClientInterceptor()
+}