added support for network policies its a breaking change

[Bloodraven21]

Summary

Adds opinionated NetworkPolicy support to the valkey chart, adapted from the Bitnami Redis chart pattern referenced in the issue. Previously networkPolicy was a bare free-form passthrough (networkPolicy: {}) requiring users to hand-write complete K8s
ingress/egress rules. This replaces it with a structured, documented config that handles the common cases out of the box while still allowing arbitrary extra rules.

What it does

When networkPolicy.enabled: true, the chart renders a NetworkPolicy that:

• Always permits intra-cluster pod-to-pod traffic on the Valkey port (required for primary/replica replication)
• Opens the metrics exporter port automatically when metrics.enabled: true
• With allowExternal: false, restricts client ingress to pods carrying the -client: "true" label, other Valkey pods, and any namespaces/pods matched by ingressNSMatchLabels / ingressNSPodMatchLabels
• With allowExternalEgress: false, limits egress to DNS and intra-cluster communication
• Appends extraIngress / extraEgress rules verbatim for custom needs

Disabled by default — no behavior change unless opted in.

[Bloodraven21]

issue
#156