[AbilityBot] DEFAULT constant is protected in AbilityBot class

[LukasPrediger]

In order to declare a "default" Ability, the name has to be set to the string "default". According to the docs theres a handy Constant for this called DEFAULT. This constant is protected and therefore not useable in AbilityExtensions

See: https://github.com/rubenlagus/TelegramBots/blob/b03fe98798192840402168e6e422d1b4cee48279/telegrambots-abilities/src/main/java/org/telegram/abilitybots/api/bot/BaseAbilityBot.java#L88