Upgrade to Next 15

## Basic Information
- Instrumentation hook is now stable, meaning Sentry can finally catch the serverside errors better
- Next won't cache pages by default. Helps with cases where user signs out and hits the back button
- Other shit like fetch not cached by default
- headers() is now awaitable. Look at PPR to make more of the page load statically
- Generate a new t3 app and check to see if anything has changed

## Other Information
- Wait a bit for compat