document usage with K8S cluster-autoscaler

[santosr2]

Note

This issue is imported from the original repository: airflow-helm#302

We should write a new FAQ section about How to use airflow with K8S cluster-autoscaler?.

This new section should cover things like:

• discussion specific to cloud-vendor cluster-autoscaler configs:
  • GKE will only respect 10min terminationGracePeriodSeconds
  • ...
• implications of using CeleryExecutor:
  • gracefully shutdown of worker pods for running tasks)
  • considerations with safeToEvict values
• example configs for the various podDisruptionBudget values
  • (to allow autoscaling to actually happen)
• interaction with KEDA
  • (once implement KEDA (autoscaler for celery workers) airflow-helm/charts#103 is resolved)
• ...