Feature request/Proposal: transparent gpg encryption

ccing @kyle.rankin @craftyguy

Based on the conversation had last night, I wanted to record it here.

Craftguy and I were able to exchange gpg excrypted messages over MMS through Chatty. It was a manual intensive process, but it worked (use a CLI program to import keys, encrypt manually, save to a file, send the file via MMS)! Upon further discussion, the actual protcol over which the gpg message works doesn't matter too much, as it gpg (seems to be) text based, so one could send gpg messages over SMS/MMS (being aware of the limitations, like size), Matrix, or any other protocol that Chatty supports.

It would be really neat if there was a way to transparently support gpg encryption to contacts. So if I wanted to send Craftyguy or kyle a message, I could have their gpg key preloaded and it could automaticaly encrypt and send the message encrypted/signed, and on the receiving end, it would recognize the PGP preamble and auto decrypt/sign. This could be transport medium agnostic as well.

SMS might be the hardest to do, as MM has a limit of ~3500 characters: https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/issues/428 , but that still allows for (shorter) plain text messages.

There could also be a way to trust/verify it offline/in person/some other way? Signal does this, you can view the key fingerprint and verify it in person.