Add subscribe button

[lad6558]

Summary

Frontend & Database Update to Allow User Subscription to "DormScoop"

Questions

• I am not sure whether the API should be set up that way. I had to allow a GET request to sustain user subscription status so that when a subscribed user refreshes the page they will see "Unsubscribe"
• I did that using a useEffect. However that has lagging, so I used a slightly hacky method to hide the button until things are loaded, and have some empty padding to keep spacing consistent
• I refactored the loading.gif out to display a random tip with it. I couldn't figure out how to sync the randomness so I went with a deterministic tip for now.

[ma-chengyuan]

For random loading tips, have you checked https://nextjs.org/docs/messages/react-hydration-error? We can probably disable SSR on <Loading/> or use useEffect to apply the randomness.

For getting the subscription status, the current hacky way looks good to me. Have you considered setting some placeholder text on the button (e.g. "loading subscription status") instead of hiding it?

Everything else lgtm.