Add support for Tinkerbell for bare metal provisioning (and Equinix Metal)

[vielmetti]

Tinkerbell (https://tinkerbell.org) is a CNCF sandbox project for bare metal provisioning,
based on the provisioning system in use at Equinix Metal.

We'd like to see Alma Linux running on Equinix Metal, and also support testing and
deploying it on various bare-metal configurations.

There is an existing open issue at tinkerbell/crocodile#8 and
a PR that addresses it at tinkerbell/crocodile#7 for an initial
round of support. The real work is likely to be as much documentation as code.

Tinkerbell expects a ".raw" file to boot from, which can be either provided by
the Alma Linux project directly, or derived from the existing ".iso".