create shared niri config, refactor generic feature modules

modules/docs.nix

@@ -118,12 +118,7 @@ in {
     options.features.documentation = let
       defaultPort = "8080";
     in {
-      enable = lib.mkOption {
-        type = lib.types.bool;
-        description = "Whether to enable documentation for the flake, generated with [Material for mkDocs](https://squidfunk.github.io/mkdocs-material/) and hosted by (containerised) nginx at localhost:${defaultPort} by default.";
-        default = true;
-      };
-
+      enable = lib.mkEnableOption "documentation for the flake, generated with [Material for mkDocs](https://squidfunk.github.io/mkdocs-material/) and hosted by (containerised) nginx at localhost:${defaultPort} by default.";
       port = lib.mkOption {
         type = lib.types.str;
         description = "This option sets the port used by the nginx server hosting the local documentation site.";