Promtail: Allow additional scrape targets

nixos/modules/monitoring/exporters/promtail.nix

@@ -28,6 +28,13 @@ in {
       # https://whetstone.private.storage/privatestorage/PrivateStorageio/-/merge_requests/258
       default = "http://172.23.23.1:3100/loki/api/v1/push";
     };
+    extraScrapeConfigs = lib.mkOption {
+      type = lib.types.listOf lib.types.attrs;
+      description = ''
+        Additional scrape configs.
+      '';
+      default = [ ];
+    };
   };
 
   config = lib.mkIf cfg.enable {
@@ -76,7 +83,7 @@ in {
           source_labels = [ "__journal__systemd_unit" ];
           target_label = "unit";
         }];
-      }];
+      }] ++ cfg.extraScrapeConfigs;
     };
   };
 }