fix: Increase connection pool to 20 concurrent database connections

Due to the asynchronous nature of FastAPI and the number of requests,
it can happen that we have to handle more than the default of 5 requests
at the same time.

backend/capellacollab/core/database/__init__.py

@@ -15,6 +15,7 @@
 engine = sa.create_engine(
     config.database.url,
     connect_args={"connect_timeout": 5, "options": "-c timezone=utc"},
+    pool_size=20,
 )
 SessionLocal = orm.sessionmaker(autocommit=False, autoflush=False, bind=engine)