Add Convos as an installable app

Convos is a popular IRC web client similar to The Lounge, which is already offered on Ultra. But it’s a more modern approach to IRC with many convenience features not available in Lounge. Most people use either The Lounge or Convos, with a strong preference on one over the other. Would be nice to have both as a choice. I prefer Convos myself because it makes IRC more similar to Discord:

https://convos.chat

It has an official Docker image. Releases are infrequent, so it’s low maintenance.