[bitnami/airflow] Consistency on Airflow configuration & init improvements

[juan131]

Description of the change

This PR changes how Airflow configuration is adapted based on users parameters: instead of setting a bunch of env. vars and relying on main containers' init logic to prepare the config file(s), everything (except config properties containing credentials) is prepared by the chart in the ConfigMap, then init containers are used to complete configuration with config properties containing credentials.

The goals is to ensure the airflow.cfg file is the same on every Airflow component (scheduler, worker, web server, etc.) given currently there are small discrepancies. Also, similar to #30246, applying changes related to credentials on init-containers has important benefits on bootstrapping, issues isolation and resource usage efficiency.

Benefits

• Configuration consistency
• Improved bootstrapping

Possible drawbacks

None

Applicable issues

• fixes Airflow LDAP variables are checked incorrectly containers#74359

Additional information

Other changes included:

• "wait-for-web-server` init container is replaced by "wait-for-db-migrations" which is more accurate.
• pod_template.yaml is moved to its own ConfigMap.
• Simplifications on helper libraries.

Checklist

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

[fmulero]

Great @juan131

I've just left a suggestion. Could you give it a look?

[fmulero]

Great! LGTM