docs: Add configurable Kubernetes probes to Helm chart docs

[claudespice]

Summary

• Add livenessProbe, readinessProbe, and startupProbe to the Common Parameters table
• Update the Health and Readiness section with configurable probe defaults and customization examples

Source PRs

• fix: make Helm chart probes configurable spiceai#10696 — fix: make Helm chart probes configurable

Changes

• website/docs/deployment/kubernetes/helm/index.md:
  • Added three new rows to the Common Parameters table for probe configuration
  • Rewrote the Health and Readiness section to show default probe values (including timeoutSeconds, periodSeconds, failureThreshold)
  • Added a "Customizing Probes" subsection with override examples, including the exec/tcpSocket/grpc fallback behavior

Test plan

• Default values match values.yaml in spiceai/spiceai
• Links are valid
• Only vNext docs updated

[github-actions]

✅ Pull with Spice Passed

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• ✅ Title meets minimum length requirement (10 characters)
• ✅ Has at least one of the required labels: area/blog, area/docs, area/cookbook, dependencies
• ✅ No banned labels detected
• ✅ Has at least one assignee: lukekim, claudespice

[github-actions]

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