Make gateway Helm chart pod/service metadata and scheduling fully configurable

Description

The gateway-helm-chart does not expose several pod-, service-, and resource-level customization knobs that customer setups commonly require, and it has two correctness bugs in how labels and annotations are rendered.

Bugs

• Duplicate label keys: setting the same key in commonLabels and a component's deployment.labels/podLabels renders duplicate YAML map keys, which strict parsers and GitOps tools (ArgoCD, kubeconform) reject. Labels should be merged with a clear precedence instead of appended.
• Inconsistent annotation precedence: at resource level commonAnnotations silently wins over per-resource annotations, while at pod level the per-resource value wins. Per-resource annotations should win consistently everywhere.

Missing configuration support (controller + gateway-runtime)

• topologySpreadConstraints, deployment strategy, terminationGracePeriodSeconds, hostAliases, dnsPolicy/dnsConfig, and pod-level automountServiceAccountToken.
• Optional startupProbe (controller template has no support; runtime value is undocumented).
• Service tunables: clusterIP, externalTrafficPolicy, loadBalancerClass, loadBalancerSourceRanges, ipFamilyPolicy/ipFamilies, and static nodePorts.* (type-gated so they only render on capable Service types).
• app.kubernetes.io/name in the standard label set.
• PVC labels/annotations (e.g. helm.sh/resource-policy: keep).
• commonLabels/commonAnnotations applied to every resource the chart renders (ServiceAccount, HPAs, PDBs, PVC, Certificate, Issuer, and the ConfigMaps are currently missed), with per-resource values winning on key conflicts.

Out of scope: extraContainers/sidecar injection on the gateway-runtime pod (tracked separately).

Version

No response

Related Issue

Equivalent APK chart change: wso2/apk#3324.