fix(database): use the request-based database sessions provided by flask-sqlalchemy
Currently the database session is created during application startup and is used in all threads. This is problematic, since the session is not thread-safe. Now we use the request-based database session provided by flask-sqlachemy instead. But this does not really solve the problem of using the same session in different threads, since the threads are started within a request.
lars-93-short-lived-database-sessions in 1 minute and 22 seconds (queued for 3 seconds)1 job for