Messaging connectors to help teams migrate to Buzz

**Motivation**
One of the main reasons I would want this is to make it easier to move my team over to Buzz.

Right now, our conversations are spread across tools like Slack, Discord, Telegram, and possibly others. It would be hard to move everyone over all at once, especially if people still need to watch the old platforms for messages.

It would be really useful if messages from those platforms could come into Buzz automatically. That way, the team could start using Buzz as the main place for communication without missing anything during the transition.

I think this could also be useful for other teams that want to move to Buzz gradually instead of doing a full switch all at once.

**Proposed solution**
Add a connector system for external messaging platforms such as Slack, Discord, Telegram, and Microsoft Teams.

At first, this could allow messages from those platforms to show up inside a Buzz channel. Ideally, replies from Buzz could also be sent back to the original platform.

It would be nice if this was built as a general connector system, rather than separate one-off integrations, so more platforms could be added later by the community.