feat: add dnsdist metrics

[cc-datum]

Summary

This PR wires DNS observability into the pdns-auth StatefulSet by fronting PDNS with dnsdist and emitting dnstap streams to two agents:

• dns-collector sidecar: consumes dnstap on :6000, applies its built-in normalizers/latency/suspicious detection, and forwards JSON to Vector.
• vector agent: consumes dns-collector JSON on :6001 (socket source), lightly normalizes labels via VRL, and exposes Prometheus metrics (queries/responses/latency/cache/NXDOMAIN/SERVFAIL/DNSSEC).

An optional lightweight monitoring stack (Prometheus + Loki + Grafana with dashboards) is provided under config/monitoring to visualize the metrics/logs.

Motivation

We already reconcile DNSZone/DNSRecordSet into PDNS via the API, but we need end-to-end visibility of real DNS traffic.
The goal is to capture, enrich, and ship dnstap events to Telemetry & Observability backends.

High-level architecture

flowchart LR
  subgraph System["dns-agent-system namespace"]
    subgraph StatefulSet["pdns-auth StatefulSet"]
      DNSDIST["dnsdist<br/>:53"]
      PDNS["PDNS Auth<br/>:5300"]
      COLLECTOR["dns-collector<br/>:6000→Vector"]
      VECTOR["vector agent<br/>:6001/:9598"]
    end
    SERVICE["Service pdns-auth<br/>:53 + vector metrics"]
  end

  subgraph Monitoring["monitoring"]
    PROM["Prometheus"]
    LOKI["Loki"]
    GRAF["Grafana"]
  end

  CLIENT["DNS clients"] -->|DNS 53| SERVICE --> DNSDIST -->|DNS 5300| PDNS
  DNSDIST -->|dnstap 6000 JSON| COLLECTOR -->|dnstap JSON 6001| VECTOR
  DNSDIST -->|metrics| PROM 
  COLLECTOR -->|metrics| PROM
  VECTOR -->|metrics| PROM
  VECTOR -.->|optionally send logs| LOKI
  PROM --> GRAF
  LOKI --> GRAF

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