Switching over the base image from Alpine to Debian

[multani]

Hello,

Due to several issues with Alpine-based images, I'm intending to switch the base image from Alpine to Debian, something more like one expects to find on an actual server where Nomad runs.

This should (finally!) open up the ability to have arm64 images and prevent this kind of issue from happening.

I intend to:

• Switch the default images multani/nomad and ghcr.io/multani/nomad to be Debian-based
• Keep a Alpine-based image, but with a dedicated -alpine-suffixed tag