[bitnami/airflow] Add support to setup db on k8s job

[juan131]

Description of the change

This PR adds support for setting up the database on a k8s job instead of relying on the Webserver setup logic.

Benefits

• Decoupling init logic from Webserver setup.
• Improve bootstrapping.

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)