[antlir2] Allow Select for dirs in ensure_dirs_exist()

Summary: **ensure_dirs_exist()** is a wrapper for **ensure_subdirs_exist()** that already supports *Select* input, let's just allow using it.

Test Plan: tested in the following diff

Reviewed By: vmagro

Differential Revision: D64907057

fbshipit-source-id: b2cc412112d30269e75c164dddd35cc65f2fcb31

antlir/antlir2/features/ensure_dir_exists/ensure_dir_exists.bzl

@@ -50,7 +50,7 @@ def ensure_subdirs_exist(
 
 def ensure_dirs_exist(
         *,
-        dirs: str,
+        dirs: str | Select,
         mode: int | str = 0o755,
         user: str = "root",
         group: str = "root"):