Add optional PodDisruptionBudgets to lagoon-core

[anothertobi]

The lagoon-core chart has multiple services that can run with a replicaCount > 1. To make them more resilient to cluster operations an optional PodDisruptionBudget (PDB) per service would be great.

Scenario

For the API service 5 pods are running in parallel. Multiple nodes need to be drained and it happens that all nodes running the API pods are drained at once. Without PDBs the API will be down. With a PDB setting minAvailable: 2 the eviction of the last two remaining pods will be blocked until new API pods start up and become ready.

Resources

• https://kubernetes.io/docs/concepts/workloads/pods/disruptions/#pod-disruption-budgets
• https://kubernetes.io/docs/tasks/run-application/configure-pdb/