Make api a Go sub-module

Allow the api to stay at the same v1 go package name and keep using a
1.x version number. This indicates the API is still at 1.x and allows
sharing proto types with containerd 1.6 and 1.7 releases.

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

core/leases/proxy/manager.go

@@ -19,7 +19,7 @@ package proxy
 import (
 	"context"
 
-	leasesapi "github.com/containerd/containerd/v2/api/services/leases/v1"
+	leasesapi "github.com/containerd/containerd/api/services/leases/v1"
 	"github.com/containerd/containerd/v2/core/leases"
 	"github.com/containerd/containerd/v2/pkg/protobuf"
 	"github.com/containerd/errdefs"