treewide: add bool type to enable options, or make use of mkEnableOption

Add missing type information to manually specified enable options or replace them by mkEnableOption where appropriate.

nixos/modules/services/system/kerberos/default.nix

@@ -51,12 +51,7 @@ in
   ###### interface
   options = {
     services.kerberos_server = {
-      enable = mkOption {
-        default = false;
-        description = ''
-          Enable the kerberos authentification server.
-        '';
-      };
+      enable = lib.mkEnableOption "the kerberos authentification server";
 
       realms = mkOption {
         type = types.attrsOf (types.submodule realm);

nixos/modules/services/system/localtime.nix

@@ -8,6 +8,7 @@ in {
   options = {
     services.localtime = {
       enable = mkOption {
+        type = types.bool;
         default = false;
         description = ''
           Enable <literal>localtime</literal>, simple daemon for keeping the system

nixos/modules/services/system/uptimed.nix

@@ -10,6 +10,7 @@ in
   options = {
     services.uptimed = {
       enable = mkOption {
+        type = types.bool;
         default = false;
         description = ''
           Enable <literal>uptimed</literal>, allowing you to track