This adds NixOS configuration for the machine whitby.tvl.fyi.
No interesting services are configured yet, so this configuration is
quite plain.
Change-Id: I67b7c75ebd6e298719b52e6b3bd83cc3be3c45d8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/843
Tested-by: BuildkiteCI
Reviewed-by: BuildkiteCI
Reviewed-by: isomer <isomer@tvl.fyi>
Reviewed-by: lukegb <lukegb@tvl.fyi>