Use of sqlite instead of dockerized postgres

[probablyVincentIp]

What

At this time the tutorial (chapter 5) uses a dockerized postgres db, I suggest to simplify this to use a sqlite db

Why

1. Sqlite is easier and faster to setup than a dockerized postgres db
2. The database type is irrelevant as Prisma has connectors for sqlite, postgres and mysql, and changing one for the other would not change the Nexus part of the tutorial meaning it would be less confusing for newcomers and and the tutorial would be more focused on Nexus itself.

How

Remove the Postgres/docker section, replace by sqlite setup. I'm happy to create a PR with this change.

[jasonkuhrt]

@supermooshman that won't transition well to deployment chapter. I understand it might seem to make not difference now. Thoughts?

[Sytten]

Point 2 is not very valid, some types are not supported in sqlite like enum and Json.