Account alias

[erlend-sh]

We need a way to support account aliases, I.e. Also-known-as sub-accounts.

Once we’ve got bridges for Discord and Matrix, everyone will have bot-accounts created for them.

If I’ve signed up to a Roomy instance that’s bridged to Discord (which I’ve also got an active account on), I should get to tie these accounts together to certify my ownership of my representative bot accounts.

This may even be possible to automate, since Discord supports Bluesky connections.