feat(cloudnative-pg): add operator PodDisruptionBudget support #1003

Problem

The cloudnative-pg chart does not currently create a PodDisruptionBudget for the operator Deployment. This leaves operator replicas unprotected during voluntary disruptions such as node drains.

This is separate from PodDisruptionBudgets for PostgreSQL clusters, which CloudNativePG manages through the Cluster spec.

Proposed approach

Add an opt-in policy/v1 PodDisruptionBudget for the operator Deployment with:

• support for either minAvailable or maxUnavailable as a count or percentage, including zero
• support for unhealthyPodEvictionPolicy
• preservation of the chart namespace, standard labels, and common annotations
• disabled-by-default behavior for backward compatibility

With the feature enabled, a default of minAvailable: 1 would protect the default single-replica operator. Deployments with additional replicas could tune the availability setting as appropriate.

Would maintainers agree with this scope and approach?

Prior and current work

• Previous implementation attempt: feat(cloudnative-pg): Setup optional PDB #639
• Current implementation for review: feat(cloudnative-pg): add operator pod disruption budget #998