nginx module: add index and tryFiles

nixos/modules/services/web-servers/nginx/default.nix

···
   mkLocations = locations: concatStringsSep "\n" (mapAttrsToList (location: config: ''
     location ${location} {
       ${optionalString (config.proxyPass != null) "proxy_pass ${config.proxyPass};"}
+      ${optionalString (config.index != null) "index ${config.index};"}
+      ${optionalString (config.tryFiles != null) "try_files ${config.tryFiles};"}
       ${optionalString (config.root != null) "root ${config.root};"}
       ${config.extraConfig}
     }

nixos/modules/services/web-servers/nginx/location-options.nix

···
       default = null;
       example = "http://www.example.org/";
       description = ''
-        Adds proxy_pass directive and sets default proxy headers Host, X-Real-Ip
-        and X-Forwarded-For.
+        Adds proxy_pass directive.
+      '';
+    };
+
+    index = mkOption {
+      type = types.nullOr types.str;
+      default = null;
+      example = "index.php index.html";
+      description = ''
+        Adds index directive.
+      '';
+    };
+
+    tryFiles = mkOption {
+      type = types.nullOr types.str;
+      default = null;
+      example = "$uri =404";
+      description = ''
+        Adds try_files directive.
       '';
     };