Request: remote builder for NGI Hydra

[tomberek]

Context

The NGI Hydra at https://hydra.ngi0.nixos.org/ is being underutilized, but can help test work on CA derivations and help promote Hydra maintenance. @Ericson2314 and I are looking at using the NGI Hydra machine to test Hydra PRs. In particular we'd like to exercise the remote builder subsystem. For this we'd like to have a remote builder.

Requirements

• ssh access from ngi machine
• no other keys/secrets
• 4 vCPU min
• root ssh access by @Ericson2314 (to allow us to test various client/server combinations)

nice to have

• aarch64-linux (to help exercise cross-system management)