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>

cmd/ctr/commands/commands_unix.go

@@ -21,8 +21,8 @@ package commands
 import (
 	"errors"
 
-	"github.com/containerd/containerd/v2/api/types/runc/options"
-	runtimeoptions "github.com/containerd/containerd/v2/api/types/runtimeoptions/v1"
+	"github.com/containerd/containerd/api/types/runc/options"
+	runtimeoptions "github.com/containerd/containerd/api/types/runtimeoptions/v1"
 	"github.com/urfave/cli/v2"
 )