feat: Add PodDisruptionBudget support with configuration options

[SweetOBurritO]

This pull request introduces support for configuring a Kubernetes PodDisruptionBudget (PDB) for Valkey replica deployments, enhancing high availability during voluntary disruptions (such as node drains or rolling updates) requested in #105 . The changes include new configuration options, Helm template logic, documentation updates, schema validation, and comprehensive tests.

PodDisruptionBudget support for high availability:

• Added a new podDisruptionBudget configuration block in values.yaml to allow enabling/disabling PDB, setting minAvailable or maxUnavailable, and specifying unhealthyPodEvictionPolicy for Valkey replicas.
• Updated values.schema.json to validate the new podDisruptionBudget fields, supporting both integer and percentage values for minAvailable and maxUnavailable, and restricting unhealthyPodEvictionPolicy to valid options.
• Created a Helm template poddisruptionbudget.yaml that conditionally generates a PDB resource when both podDisruptionBudget.enabled and replica.enabled are true, applying the configured settings and selector labels.

Documentation updates:

• Added a "High Availability" section to README.md explaining how to enable and configure PodDisruptionBudget, including usage examples and important notes about its behavior.
• Extended the configuration table in README.md to document the new podDisruptionBudget fields and their purposes.

Testing:

• Introduced a new test suite poddisruptionbudget_test.yaml with comprehensive cases to verify correct PDB creation, field precedence, value types, label propagation, and custom name overrides.

[sgissi]

Amazing work @SweetOBurritO, thanks for the PR. A few nitpicks in my review below, nothing major. Have you already tested that PDB works as intended for both min and max settings?

[SweetOBurritO]

@sgissi Updated the PR to address your feedback, simplified the documentation and fixed the values comments.

[amontalban]

Looking forward to have this feature merged in 🙏

[SweetOBurritO]

Hi @sgissi , just checking in on this PR, I know maintainers are often busy, so no rush.

Would you mind letting me know if there’s any feedback, changes, or additional info needed from my side to help move this forward?