Update to /repos command group

[49Indium]

A few changes to the /repos command group:

• Changed list and find to run as embeds
• Added issues, which lists the issues of a specific repo
• Added prs, which lists the PRs of a specific repo

This will require a new auth token in the bot for github API access, which is given by an environment variable. I will update the wiki soon.

[andrewj-brown]

Also converted to draft while we figure out what to do with tokens.