Update sandbox API to return target platform

Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>

sandbox/controller.go

@@ -20,6 +20,7 @@ import (
 	"context"
 
 	"github.com/containerd/containerd/api/services/sandbox/v1"
+	"github.com/containerd/containerd/api/types"
 )
 
 // Controller is an interface to manage sandboxes at runtime.
@@ -30,6 +31,9 @@ type Controller interface {
 	Create(ctx context.Context, sandboxID string) error
 	// Start will start previously created sandbox.
 	Start(ctx context.Context, sandboxID string) (*sandbox.ControllerStartResponse, error)
+	// Platform returns target sandbox OS that will be used by Controller.
+	// containerd will rely on this to generate proper OCI spec.
+	Platform(_ctx context.Context, _sandboxID string) (*types.Platform, error)
 	// Stop will stop sandbox instance
 	Stop(ctx context.Context, sandboxID string) (*sandbox.ControllerStopResponse, error)
 	// Wait blocks until sandbox process exits.