[helm] Add pod annotations, pod labels, and PodDisruptionBudget support

[fresh-borzoni]

Search before asking

• I searched in the issues and found nothing similar.

Description

The Fluss Helm chart is missing standard Kubernetes pod-level configuration that production deployments rely on.

There is currently no way to add custom annotations to pods (needed for Prometheus scraping, Vault agent injection, Datadog, etc.), no way to add custom labels (needed for service mesh routing, monitoring selectors), and no PodDisruptionBudget to protect against draining too many replicas during rolling upgrades or node maintenance.

Willingness to contribute

• I'm willing to submit a PR!