File containing the sticker.
For normal stickers: must be a .png or .webp file
up to 512kb, having both dimensions <=512px, and having
one of the dimensions ==512px
For animated stickers: must be a .tgs file
up to 64kb, having canvas dimensions exactly
512x512px, duration no more than 3 seconds
and animated at 60fps (source)
OptionalmaskIn case this is a mask sticker, position of the mask
One or more emojis that represent this sticker