Add Alma Linux support

[vielmetti]

Expected Behaviour

Add support for Alma Linux, which is a drop-in replacement for CentOS that's under development.

Current Behaviour

PR #7 has some changes, including building a raw file from the distributed ISO,
and putting together a kickstarter script.

Possible Solution

Test against the patches in #7 .

Context

CentOS (classic) is EOL at end of year, so this effort is designed to support
testing and development of an alternative. There may emerge several alternatives
to CentOS and we want to make testing and validation of each of them as
easy as possible.

Your Environment

• Operating System and version (e.g. Linux, Windows, MacOS):

Alma Linux

• How are you running Tinkerbell? Using Vagrant & VirtualBox, Vagrant & Libvirt, on Packet using Terraform, or give details:

• Link to your project or a code example to reproduce issue:

The main Alma Linux repo is at https://github.com/AlmaLinux/cloud-images and the corresponding issue there is AlmaLinux/cloud-images#7