Replace lib/hosts.nix with an injected special argument containing the nix flake

hosts/monitoring-3/prometheus.nix

@@ -1,9 +1,9 @@
-{ config, pkgs, lib, ... }:
+{ config, pkgs, lib, _nixfiles, ... }:
 
 with lib;
 
 let
-  hosts = (import ../../lib/hosts.nix { inherit pkgs; }).hosts;
+  hosts = _nixfiles.nixosConfigurations;
 
   monitoringHosts = filterAttrs (name: host:
     attrByPath ["clerie" "monitoring" "enable"] false host.config)