feat(Message): new message types

[Victorsitou]

Summary

discord/discord-api-docs#5815

I don't know what's the content of interaction_premium_upsell and guild_application_premium_subscription, neither their description, so I left it as TBD. Also, it seems that stage_raise_hand isn't shown in the UI (that's why I didn't add it to Message.system_message)

Checklist

• If code changes were made, then they have been tested
  • I have updated the documentation to reflect the changes
  • I have formatted the code properly by running task lint
  • I have type-checked the code by running task pyright
• This PR fixes an issue
• 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, ...)

[shiftinv]

Looks good so far!
Good catch on the MessageType literal, looks like that one was slightly outdated.

Regarding system_content:

• Type 26 is the message type of an (ephemeral?) interaction response that can be sent by applications with premium subscriptions; that one should just be return self.content, as far as I can tell.
• Type 32 should be something like f"{self.author.name} upgraded {application_name} to premium for this server! 🎉", where application_name is self.application.get("name") if present, or "a deleted application" if not.

[shiftinv]

lgtm