Migrate Telegram bridge to Matterbridge
We currently use teleirc for the Telegram-IRC bridge, which is unmaintained, so we should replace it with something else. appdeia tested matterbridge and it seemed to work well.
Since the config file will now have group IDs instead of names, which are non-trivial for users to figure out, and we can't easily split the channel list from the other configuration (including passwords and tokens), we may have to make it not self-service anymore. That is, the channel list would be in a sysadmin-only repo.
I plan to have this fully ansible-managed.
(moved from https://phabricator.kde.org/T13071)