nixos/charybdis: implement reload functionality

IRC daemons are highly stateful daemons, so allow config changes without
kicking all server and client connections.

Basically a port of 60c62214f5.

nixos/modules/services/networking/charybdis.nix

@@ -85,14 +85,21 @@ in
         "d ${cfg.statedir} - ${cfg.user} ${cfg.group} - -"
       ];
 
+      environment.etc."charybdis/ircd.conf".source = configFile;
+
       systemd.services.charybdis = {
         description = "Charybdis IRC daemon";
         wantedBy = [ "multi-user.target" ];
+        reloadIfChanged = true;
+        restartTriggers = [
+          configFile
+        ];
         environment = {
           BANDB_DBPATH = "${cfg.statedir}/ban.db";
         };
         serviceConfig = {
-          ExecStart   = "${charybdis}/bin/charybdis -foreground -logfile /dev/stdout -configfile ${configFile}";
+          ExecStart   = "${charybdis}/bin/charybdis -foreground -logfile /dev/stdout -configfile /etc/charybdis/ircd.conf";
+          ExecReload = "${coreutils}/bin/kill -HUP $MAINPID";
           Group = cfg.group;
           User = cfg.user;
         };