Fix: field change from thumb to thumbnail since Bot API 6.6

[0x114514BB]

• [ ] All tests pass (I did't run tests since I have no payment provider token yet)
• [x] I have run npm run doc

Description

As Bot API 6.6 changelog said,

Renamed the field thumb in the classes Animation, Audio, Document, Sticker, Video, VideoNote, InputMediaAnimation, InputMediaAudio, InputMediaDocument, InputMediaVideo, StickerSet to thumbnail.

But the field thumb in _fixAddFileThumbnail function remains unchanged.

Users won't be able to add thumbnail in sendAudio and similar functions if they follow the official API documents unless they use old thumb.

P.S. Users of NTBA also need to update their code since the field change. I wonder whether NTBA's documentation should notice this change or not.

References

Telegram Bot API Changelog 2023-03-09

[guoyunhe]

This is cool! @yagop can you merge it?