Handle access-blocked GitHub integrations

[kitallis]

Problem

On GitHub

The integration was attempted but the request is pending because the users do not have permissions to grant access to the Tramline + Github app to their workspace.

Elsewhere

It's possible that other integrations also suffer from this, so it's worth access-blocking and testing them out to ensure that they fail gracefully.

Steps to Reproduce

Add a user to GH and remove their permission to grant app access.

Expected behavior

We should either: 1) Return back to Tramline saying that this needs to be reconnected 2) It should gracefully fail the connect