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>

contrib/fuzz/builtins_linux.go

@@ -18,7 +18,7 @@ package fuzz
 
 import (
 	// Linux specific imports
-	_ "github.com/containerd/containerd/v2/api/types/runc/options"
+	_ "github.com/containerd/containerd/api/types/runc/options"
 	_ "github.com/containerd/containerd/v2/core/metrics/cgroups"
 	_ "github.com/containerd/containerd/v2/core/metrics/cgroups/v2"
 	_ "github.com/containerd/containerd/v2/plugins/snapshots/blockfile/plugin"