feat: support oxia metadata store

[mattisonchao]

Motivation

• Support Oxia as an in-cluster metadata provider for sn-platform and sn-platform-slim without requiring users to configure service addresses manually.
• Keep ZooKeeper as the default metadata provider and preserve existing ZooKeeper compatibility.
• Ensure bundled Prometheus can scrape both Oxia dataserver and coordinator metrics without requiring Prometheus Operator.

Modifications

• Added pulsar_metadata.provider support for zookeeper and oxia, with validation for ZooKeeper-only fields.
• Added OxiaCluster and OxiaNamespace templates using Oxia 0.16.6 and split namespaces for broker, bookkeeper, pulsar-schema, and function.
• Added optional oxia chart values for custom labels, annotations, server replica count, dataserver resources, and coordinator resources.
• Wired broker, BookKeeper, schema storage, and function-worker config to use Oxia metadata URLs when provider is Oxia.
• Gated ZooKeeper resources so they are not rendered for Oxia metadata deployments.
• Added bundled Prometheus scrape config job_name: oxia that scrapes both metrics and coord-metrics ports.
• Gated Oxia monitoringEnabled on the availability of the PodMonitor API so sn-operator only creates PodMonitor when Prometheus Operator CRDs exist.

Documentation

• No standalone docs page is required for this PR. The user-facing chart knobs are documented in the chart values.yaml, and examples/sn-platform/values-oxia.yaml shows the minimal Oxia enablement path.

Testing

• helm lint charts/sn-platform-slim -f examples/sn-platform/values-oxia.yaml --set istio.enabled=true --set monitoring.prometheus=true --set monitoring.grafana=false
• helm lint charts/sn-platform -f examples/sn-platform/values-oxia.yaml --set istio.enabled=true --set monitoring.prometheus=true --set monitoring.grafana=false
• helm lint for the sn-platform and sn-platform-slim CI values.
• helm template for both chart variants with Oxia values.
• Rendered OxiaCluster overrides for labels, annotations, replicas, dataserver resources, and coordinator resources.
• Verified oxia.replicaCount < 3 fails template validation for Oxia metadata deployments.
• Local kind deployment with sn-operator v0.18.10, Istio ambient, no proxy, Oxia 0.16.4, and bundled Prometheus.
• Verified Pulsar producer/consumer smoke test through a perf pod.
• Verified bundled Prometheus ingests oxia_dataserver_* and oxia_coordinator_* series under job=oxia.
• Final chart review after the Oxia 0.16.6 default image bump: helm lint and helm template passed for both chart variants, including minimal Oxia values and explicit dataserver/coordinator resource overrides.

[github-actions]

@mattisonchao:Thanks for your contribution. For this PR, do we need to update docs?
(The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)

[Copilot]

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[mattisonchao]

Documentation info has been added to the PR description. The chart knobs are documented in values.yaml, and examples/sn-platform/values-oxia.yaml shows the minimal Oxia enablement path.