Add integration tests on server

[charlesBochet]

We don't have tests on server right now which will lead to regressions.
As our first testing strategy, we would like to put in place integration tests: create test suite that will query the API and use a seeded postgres database

Todo:

• find a way to provision a testing postgres database locally (maybe just create a test database on the existing instance?)
• find a way to provision a testing prostgres database in CI
• write a script to seed the test database before running the tests
• write a first test suite. Make sure it's idempotent