nixos/modules: Remove all usages of types.string

And replace them with a more appropriate type

Also fix up some minor module problems along the way

nixos/modules/services/security/oauth2_proxy_nginx.nix

@@ -6,14 +6,14 @@ in
 {
   options.services.oauth2_proxy.nginx = {
     proxy = mkOption {
-      type = types.string;
+      type = types.str;
       default = config.services.oauth2_proxy.httpAddress;
       description = ''
         The address of the reverse proxy endpoint for oauth2_proxy
       '';
     };
     virtualHosts = mkOption {
-      type = types.listOf types.string;
+      type = types.listOf types.str;
       default = [];
       description = ''
         A list of nginx virtual hosts to put behind the oauth2 proxy