Matterbridge: [General] Support user typing messages

[patcon]

A meta-issue for researching and figuring out "user typing" message cross-compatibility.

• [x] Discord Docs 1 2 https://github.com/42wim/matterbridge/pull/914
• [ ] Gitter TBD Feature Request
• [ ] Matrix/Riot Docs
• [ ] Mattermost Docs
• [ ] RocketChat Docs
• [x] Slack
• [ ] Telegram Docs
• [ ] XMPP (technically supported in spec, but TBD)
• [ ] Zulip Docs
• [ ] IRC Docs (h/t @westor7)
• [ ] WhatsApp (Docs?)

[qaisjp]

Discord need tick

[Heath123]

Should WhatsApp be in this list?

[westor7]

IRC could either be in the list -> https://ircv3.net/specs/client-tags/typing