feat: enhance Blackbox Exporter configuration with domain blacklist and update Grafana alerting rules

hosts/web-arm/modules/grafana/alerting/websites/default.nix

@@ -1,9 +1,11 @@
 { lib, pkgs, config, ... }:
 
 let
+  cfg = config.services.blackbox-exporter;
   nginxVHosts = config.services.nginx.virtualHosts or {};
   allDomains = lib.attrNames nginxVHosts;
-  httpsDomains = lib.map (d: "https://${d}") allDomains;
+  filteredDomains = builtins.filter (d: !builtins.elem d cfg.blacklistDomains) allDomains;
+  httpsDomains = lib.map (d: "https://${d}") filteredDomains;
   websiteAlertRules = lib.map (target:
     let
       domain = lib.replaceStrings ["://" "." "-" "/" ] ["-" "-" "_" "_"] target + "-down-alert";