feat: add new poll system message type

[Snipy7374]

Summary

• Closes GH-1212

~~This is something new for me so i want to ask if i need to add the new fields documented in the discord PR respectively to the Embed and Message class~~

Checklist

• [x] If code changes were made, then they have been tested
  • [x] I have updated the documentation to reflect the changes
  • [x] I have formatted the code properly by running pdm lint
  • [x] I have type-checked the code by running pdm pyright
• [ ] This PR fixes an issue
• [x] This PR adds something new (e.g. new method or parameters)
• [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [ ] This PR is not a code change (e.g. documentation, README, ...)

[Snipy7374]

The "s: waiting for api/docs" label can now be removed 🙏🏻

[shiftinv]

edit: disregard this comment

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~~Seeing how the poll result embeds are currently structured, I don't think we can represent them entirely in system_message - the result (with a clear winner) looks like this, for instance:~~ ~~The closest would be something like the following, which doesn't really make sense on its own:~~

{author}'s poll {question} has closed.

{answer_text}
Winning answer • {maths}%

~~Just having the first line would be enough, in my opinion.~~