FEATURE: custom flag can require additional message (#27908)

Allow admin to create custom flag which requires an additional message.

I decided to rename the old `custom_flag` into `require_message` as it is more descriptive.

lib/flag_settings.rb

@@ -2,11 +2,11 @@
 
 class FlagSettings
   attr_reader(
-    :without_custom_types,
+    :without_additional_message_types,
     :notify_types,
     :topic_flag_types,
     :auto_action_types,
-    :custom_types,
+    :additional_message_types,
     :names,
   )
 
@@ -15,8 +15,8 @@ class FlagSettings
     @topic_flag_types = Enum.new
     @notify_types = Enum.new
     @auto_action_types = Enum.new
-    @custom_types = Enum.new
-    @without_custom_types = Enum.new
+    @additional_message_types = Enum.new
+    @without_additional_message_types = Enum.new
     @names = Enum.new
   end
 
@@ -26,7 +26,7 @@ class FlagSettings
     topic_type: nil,
     notify_type: nil,
     auto_action_type: nil,
-    custom_type: nil,
+    require_message: nil,
     name: nil
   )
     @all_flag_types[name_key] = id
@@ -35,10 +35,10 @@ class FlagSettings
     @auto_action_types[name_key] = id if !!auto_action_type
     @names[id] = name if name
 
-    if !!custom_type
-      @custom_types[name_key] = id
+    if !!require_message
+      @additional_message_types[name_key] = id
     else
-      @without_custom_types[name_key] = id
+      @without_additional_message_types[name_key] = id
     end
   end