Admin user can see two identical prompts to authenticate when setting up Canvas Studio

[robertknight]

This is a follow-up to #6139.

When launching a Canvas Studio assignment, an admin user may be presented with two successive prompts to authenticate - one prompt to authenticate with Canvas and a separate one to authenticate with Canvas Studio. Both authorization prompts look identical, so after the user completes the first auth flow (for Canvas) it may seem as though it has not worked properly and they are being presented with exactly the same prompt again. However when the user clicks "Authorize" again, they will see a different popup window, as they are prompted to authenticate with a different service.

This issue could be resolved if the authorization prompt more clearly indicated which service the user is being prompted to authenticate with. This also ties into related discussions around making the prompt more friendly.