Add ability to grep through github items (issues, comments, prs)

[cbrxyz]

We should add a hybrid command that can grep through GitHub related items in Discord. This would make it much easier to pull up relevant items in Discord, without needing to go to the GitHub website.

I'm thinking that if the app command version of the command is called, then we should post an ephemeral message. Otherwise, we should post a normal message with the relevant item.