Allow stickers to be 512x512

This is a common sticker size in other messaging applications; increasing the sticker size would allow stickers from these applications to be imported without further changes. Most notably, the resolution for Telegram Lottie stickers is 512x512; and adjusting the scale of a Lottie file is an ardruous task requiring expensive software. It would be nice if Discord could just allow using these stickers as-is.