feat: add airflow triggerer Deployment

[thesuperzapper]

What issues does your PR fix?

• resolves add airflow triggerer Deployment (support Deferrable Operators) #424
• supersedes & closes feat: add airflow triggerer Deployment  #521
  • (some further changes were needed, and I did not have write access to that repo)

What does your PR do?

• Adds a new Deployment for the airflow triggerer so we fully support Airflow's Deferrable Tasks feature.
  • WARNING: airflow triggerer was added in airflow 2.2.0, so will crash-loop if enabled in previous versions
  • NOTE: The triggerer deployment is automatically (and silently) disabled in the following situations:
    • if airflow.legacyCommands is true
    • if airflow.image.repository is apache/airflow and airflow.image.tag corresponds to an airflow version before 2.2.0
• Adds the following new values:
  • triggerer.enabled (default: true)
  • triggerer.replicas (default : 1)
  • triggerer.resources
  • triggerer.nodeSelector
  • triggerer.affinity
  • triggerer.tolerations
  • triggerer.securityContext
  • triggerer.labels
  • triggerer.podLabels
  • triggerer.annotations
  • triggerer.podAnnotations
  • triggerer.safeToEvict (default: true)
  • triggerer.podDisruptionBudget:
    • triggerer.podDisruptionBudget.enabled (default: false)
    • triggerer.podDisruptionBudget.maxUnavailable
    • triggerer.podDisruptionBudget.minAvailable
  • triggerer.capacity (default: 1000)
  • triggerer.livenessProbe:
    • triggerer.livenessProbe.enabled (default: true)
    • triggerer.livenessProbe.initialDelaySeconds (default: 10)
    • triggerer.livenessProbe.periodSeconds (default: 30)
    • triggerer.livenessProbe.timeoutSeconds (default: 60)
    • triggerer.livenessProbe.failureThreshold (default: 5)
  • triggerer.extraPipPackages
  • triggerer.extraVolumeMounts
  • triggerer.extraVolumes

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