[bitnami/airflow] feat: add support for custom local settings

[juan131]

Description of the change

This PR adds support for users to customize the local setting file, find more info at:

• https://airflow.apache.org/docs/apache-airflow/stable/howto/set-config.html#configuring-local-settings

Benefits

Support to advanced integrations during the initialization.

Possible drawbacks

None

Applicable issues

None

Additional information

N/A

Checklist

• [x] Chart version bumped in Chart.yaml according to semver. This is not necessary when the changes only affect README.md files.
• [x] Variables are documented in the values.yaml and added to the README.md using readme-generator-for-helm
• [x] Title of the pull request follows this pattern [bitnami/] Descriptive title
• [x] All commits signed off and in agreement of Developer Certificate of Origin (DCO)