feat(docs): add DNS Zone support

[YXShang97]

Summary

Adds Azure DNS Zone monitoring support to Promitor documentation.

Changes

• Added dns-zone.md provider documentation with RecordSetCapacityUtilization metric example
• Updated overview to include DNS Zone in supported services list
• Updated resource discovery documentation with DNS Zone example

Features

• Resource type: DnsZone
• Required field: zoneName
• Supports both static resources and automatic discovery
• Example metric: DNS capacity utilization monitoring

Usage

name: azure_dns_zone_capacity_utilization
description: "Percentage of record set capacity utilized by a DNS zone"
resourceType: DnsZone
azureMetricConfiguration:
  metricName: RecordSetCapacityUtilization
  aggregation:
    type: Maximum
resources:
  - zoneName: example.com

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All committers have signed the CLA.

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[YXShang97]

Several external links are now broken due to GitHub apps being archived or repositories no longer available, causing build failures. Added these URLs to htmlproofer exclusions to prevent CI/CD pipeline errors while preserving historical documentation references.