Update to iPXE version to 1.21.1

- Build additional artifacts - ISO, UEFI, etc.
- Set default timeout on shell to fallthrough on failures
- Add ping command (enabling patch renamed to be more generic)
- Update build container to Debian 11
- Add VERSION file

Change-Id: I9476c1d6446f6943dcd084384ba2ae3d96f71128
diff --git a/Dockerfile b/Dockerfile
index 7bd7f6d..65e1d75 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -3,7 +3,7 @@
 # SPDX-FileCopyrightText: © 2020 Open Networking Foundation <support@opennetworking.org>
 # SPDX-License-Identifier: Apache-2.0
 
-FROM debian:10.6
+FROM debian:11
 
 # Install Build packages
 RUN apt-get -y update \