add haproxy sysext creation script

[justdan96]

Add HAProxy Sysext Creation Script

This PR adds an HAProxy creation script to the repo. The creation has been tested and the running of the system extension tested on a VM. The script is heavily based on the keepalived script. Options and sample configurations have been pulled from AlmaLinux sources.

How to use

Just run ./create_haproxy_sysext.sh on a Linux system with Docker installed.

Testing done

Script run and system extension installed on Ubuntu system.

• Changelog entries added in the respective changelog/ directory (user-facing change, bug fix, security fix, update)
• Inspected CI output for image differences: /boot and /usr size, packages, list files for any missing binaries, kernel modules, config files, kernel modules, etc.

[tormath1]

Thanks for the PR - I'm curious, what would be the benefit here comparing to the official HAProxy Docker image: https://hub.docker.com/_/haproxy ?

[justdan96]

There aren't really benefits, it's just an alternative method for deployment. If migrating from a traditional HAProxy-on-VMs deployment this method might be easier for people to use.