Add org selection when connecting GitHub apps
Created by: pjlast
This PR addresses CLOUD-285 and CLOUD-289. If a user belongs to any GH Orgs with our GH App installed, they are presented with a list of these orgs to connect to when connecting their Org's code host connection.
Normal case (user is GH Org admin): https://www.loom.com/share/a90157b1992443ec95787d26c9e21d32
User is not a GH Org admin: https://www.loom.com/share/343925e7242349dba0d51c52b9f82516
Test plan
Manual e2e testing.