feat: adds main database using postgres and prisma

[otaviotscha]

The idea is to use Neon, but I am having the following issue:

yarn prisma migrate dev --name add_user_table

Error: db error: ERROR: database "prisma_migrate_shadow_db_4d2b9c3a-2d09-4d96-bee1-e225387463ab" is being accessed by other users
DETAIL: There is 1 other session using the database.
   0: schema_core::state::EvaluateDataLoss
             at schema-engine/core/src/state.rs:315

[otaviotscha]

Infrastructure decisions are not going to be discussed here anymore.
See #9