Sticker support!

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Is your feature request related to a problem? Please describe.
I'd love to see NextCloud Talk get support for stickers and sticker packs like on Telegram. It's such a fun way to communicate with others and gives users the ability to be creative and make their own custom stickers too!

Describe the solution you'd like
It would be awesome to see a sticker solution that works very similar to Telegram and Discord. Something where users can easily upload their own custom images and create sticker packs, and other peoples sticker packs can be clicked on and added to your personal collection.

Describe alternatives you've considered
Alternatives could be just sending images but it's awesome to have them at the ready and organised into packs, and stickers allow for fun interactions like having clever animations or dragging and dropping onto chat bubbles like in iMessage.

Additional context
No additional context!

The issue names no files, tests, or entry points. Start by mapping how Talk currently handles chat media, uploads, and saved collections, then define the sticker and pack behavior before implementation; completion criteria are not specified beyond Telegram- or Discord-like support.