Introduced with dependencies it needs, with a number of plugins disabled
that don't build with ghc-9.4.x yet.

algebraic-graphs downgraded to 0.6.1 due to incompatibility in hiedb.

This is more reliable than trying to use the previous horizon-platform
version.

Bump nixpkgs and ghc 942 -> 944

See merge request horizon/horizon-platform!42

servant-auth-client: init at 0.4.1.0

See merge request horizon/horizon-platform!46

add servant-auth and servant-auth-server

See merge request horizon/horizon-platform!45

update horizon-gen-nix and horizon-spec

See merge request horizon/horizon-platform!44

horizon-gen-nix: 0.4.0 -> 0.5