Deploy airflow with postgresql and pooling

[tgrandje]

Airflow's documentation states that setting a postgresql database in production may require PgBouncer because of an important number of connections:

• see here in Setting up a PostgreSQL Database
• see also here in production guide for helm-chart.

On the other hand, the configuration documentation states that airflow uses (by default config) a SqlAlchemy pool :

• sql-alchemy-pool-enabled : default is True
• sql_alchemy_pool_size : default is 5

That seems conflicting to me. Is any of this outdated? (I'll open an issue on this if confirmed.)