Added Prisma ORM and User Entity

[henrybrink]

This adds an initial configuration for the Prisma ORM.
It contains the user entity and a migration which creates a single database table for the user.

There will be further documentation added later to the project which will contain examples on how to repositories should be build, how they should be tested and other guidelines, but this is still an early verification phase.

[henrybrink]

I adjusted some coverage configuration with this PR because:

• Some files are not relevant for the application, but only for manual testing (seeding currently)
• Some files cannot be tested easily (main.ts, as this should normally not be changed, it is okay to not have a unit test for now)

I also decreased the required branch / function coverage, as there may be cases where we cannot really test some functions and as this is counted as global coverage it very fast fails. 80% should be better reachable, and considering the project environment it is okay.

[benedictweis]

Thank you!