Added discord context provider

[eagle3y3]

Description

I've added a discord provider. Currently it is able to read text channels. It must be installed with a bot on the server. I think it would be a very useful bridge from devs to users who like to communicate through Discord. In order to test and run it. You must have a bot token and the same bot installed onto your server. Reading threads will come soonish if there's any interest.

Checklist

• [x] The base branch of this PR is dev, rather than main
• [x] The relevant docs, if any, have been updated or created

Screenshots

Testing

[ For new or modified features, provide step-by-step testing instructions to validate the intended behavior of the change. ]