Add support for Keybase proof verification

It's just an idea but it would be great to be able to verify our discord accounts in keybase.io mainly so we can make sure people there contact correct account, given multiple accounts can have the same name distinguished only by 4 digits on end.

Before I get told its something keybase needs to do: noThis needs to be implemented by discord then discord contacts keybase and they just enable it on their end.

src about creating proofing flow:

https://book.keybase.io/guides/proof-integration-guide