Fetching all sticker emojis when adding a stciker to a pack

[zeroone2numeral2]

This needs Pyrogram to work, as we need to fetch a stciker's pack to figure out all its emojis, and this is something we can do through the raw API only.

Work can be tracked from branch sticker-emojis

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Things to do:

• [x] Pyrogram usage should be configurable from the config file
• [x] there should be a persistent pyrogram.Client instance (with updates disabled) ready to be used. Right now we use its context manager, but it's highly inefficient as we would spawn and kill a Client instance on every received sticker
• [x] check it works correctly with animated stickers too

[zeroone2numeral2]

Just realized that the methods to create a set and to add stickers to an existing set, despite requiring some "emojis" (stress on the "s"), actually care only about the first one and will ignore all the other. Fuck.

[zeroone2numeral2]

Of course, still no answer from the bot support

Edit: fixed