[skip ci] Add comments for Task interface (#12418)

Signed-off-by: yun.zhang <yun.zhang@zilliz.com>

Co-authored-by: yun.zhang <yun.zhang@zilliz.com>

internal/indexcoord/task.go

@@ -41,7 +41,7 @@ type task interface {
 	Execute(ctx context.Context) error
 	PostExecute(ctx context.Context) error
 	WaitToFinish() error
-	Notify(err error)
+	Notify(err error) // notify if task is terminated
 	OnEnqueue() error
 }