add values to specify resources on init-containers

[fogelman]

What issues does your PR fix?

• fixes add values to specify resources on init-containers #242

What does your PR do?

Allows users to specify resources for initContainers.

Checklist

For all Pull Requests

• Commits are signed off
• Commits have semantic messages
• Documentation updated
• Passes ct linting

For releasing ONLY

• Chart.yaml version bumped
• CHANGELOG.md updated

[thesuperzapper]

@fogelman This PR does not work as it currently stands (see comments from the review).

But either way, I think we should use a different approach, and have global resource values for each init-container type. This is because it does not make sense to give the worker/scheduler resources to the install_pip_packages, wait_for_db_migrations, or check_db init-containers, as they very likely do not need 2 CPU / 4GB RAM, for example.

These values might look like:

airflow:
  
  ## << put these configs JUST BEFORE the `airflow.localSettings` in the default values.yaml >>

  ## configs for the airflow init-containers
  ##
  initContainers:
    
    ## configs for the `check-db` init-container
    checkDb:
      
      ## resource requests/limits for the `check-db` init-container
      ## - spec for ResourceRequirements:
      ##   https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.20/#resourcerequirements-v1-core
      ##
      resources: {}

    ## configs for the `wait-for-db-migrations` init-container
    waitForDbMigrations:
      
      ## resource requests/limits for the `wait-for-db-migrations` init-container
      ## - spec for ResourceRequirements:
      ##   https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.20/#resourcerequirements-v1-core
      ##
      resources: {}

    ## configs for the `install-pip-packages` init-container
    installPipPackages:

      ## resource requests/limits for the `install-pip-packages` init-container
      ## - spec for ResourceRequirements:
      ##   https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.20/#resourcerequirements-v1-core
      ##
      resources: {}

This also lets us add values to disable these init-containers in future, if people like.

[thesuperzapper]

The value .resources will not be defined, you must also change every time the "airflow.init_container.check_db" template is called to include the appropriate resources.

For example, in the scheduler this might look like:

# top of file
{{- $resources := .Values.scheduler.resources }}

# in the init container section
{{- include "airflow.init_container.check_db" (dict "Release" .Release "Values" .Values "volumeMounts" $volumeMounts "resources" $resources) | indent 8 }}

[thesuperzapper]

@fogelman thanks for the PR, but I am closing in favor of #855