This reduces the confusion with the nixos/modules/deployment.nix module,
and should make it clearer that it can contain any configuration that
applies to all hosts on the grid.

This lets other modules override these settings.

This should let it work for both enabled and disabled configurations

Using AWS is what causes it so using AWS can be what fixes it, too.

... This breaks the tie, thx to https://github.com/DBCDK/morph/issues/146

... that don't have it by default. (<5.6)

This makes wireguard work on older kernels (19.09 nixos), i.e.
our storage servers currently) and newer kernels (21.05, i.e.
the monitoring server).

Fewer lines almost always better.  Also, we don't want to spread
these out unless we have to.

... we'll need this later for the TLS cert.