Feature: Add tool to list channels the authenticated user is a member of

[sonjaer]

I'd like to be able to:

• List all channels I'm a member of
• See what channels other team members are part of, so I can discover and join relevant ones
• List all channels in the org

[hello-ashleyintech]

Hi, @sonjaer! Thanks so much for submitting this request. I've forwarded it to the appropriate team internally and will drop back in with any updates.