prometheus service: add scrapeConfigs.params option

nixos/modules/services/monitoring/prometheus/default.nix

@@ -116,6 +116,13 @@ let
           The URL scheme with which to fetch metrics from targets.
         '';
       };
+      params = mkOption {
+        type = types.attrsOf (types.listOf types.str);
+        default = {};
+        description = ''
+          Optional HTTP URL parameters.
+        '';
+      };
       basic_auth = mkOption {
         type = types.nullOr (types.submodule {
           options = {