✨ Use extra pytest arguments forwarded from shell (#17)

* removed postgres_password from alembic.ini, read it from env var instead

* ♻️ use f-strings for PostgreSQL URL

* passes given args

{{cookiecutter.project_slug}}/backend/app/tests-start.sh

@@ -3,4 +3,4 @@ set -e
 
 python /app/app/tests_pre_start.py
 
-pytest /app/app/tests/
+pytest $* /app/app/tests/