Update fly + next + sqlite deployment instructions in coursebook

[sofer]

Looks like we are in a bit of a mess with deploying apps that persist data.

A mix of options that include fly.io, vercel and SQLite does not seem to work very well.

We need to get this sorted out before next time.

[ivan-unfolds]

@ivanmauricio to check this out

[ivan-unfolds]

docs for deployment on fly are split out over a few places (a blog post by oil, the projects tab in week 2). it would be better if this all lived in one place to make it easier for student's to debug their deployed apps.

also some of the issues we're facing with fly might be coming from being on the pay-as-you-go plan and reaching our limits. @sofer is going to upgrade the subscription to a launch plan and we will keep an eye on whether that makes a difference

@ivanmauricio is also going to deploy a next app on fly which uses SQLite with persistent volumes to verify that all works.