Manage pools in Helm Chart

Hello,

Many users need to deployment Airlfow and initialize instances with basic resources. It would be helpful if Helm Chart would facilitate this task.

For connections and variables, all we need to do is add documentation that describes the use of [environment variables](https://airflow.readthedocs.io/en/latest/cli-and-env-variables-ref.html#environment-variables).

For pools, we will have to add a new script that initializes the database using the CLI.
https://airflow.readthedocs.io/en/latest/cli-and-env-variables-ref.html#pools

Similar tasks can be done with [Terraform provider](https://github.com/apache/airflow/issues/10550) as well, but it's still WIP and not everyone uses Terraform. We still need better support for this use case in the Helm Chart.

Best regards,
Kamil Breguła