Add HasStableAksVersion operator to validate AKS cluster Kubernetes versions

[RazvanLoghin1]

Description

This PR introduces a new HasStableAksVersion operator to the Template Analyzer's JSON Rule Engine

This operator validates whether Azure Kubernetes Service (AKS) clusters are using stable Kubernetes versions for their deployment regions.

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Key Changes

• New Operator: HasStableAksVersionOperator evaluates AKS resources to verify they use stable Kubernetes versions.
• Version Provider System: Implemented a provider pattern with IStableAksVersionProvider interface to fetch stable versions.
• Default Implementation: DefaultStableAksVersionProvider fetches real-time stable versions from the official AKS releases API: [https://releases.aks.azure.com/webpage/parsed_data.json]
• Caching Mechanism: Thread-safe singleton implementation with lazy initialization to minimise API calls.
• Registry Pattern: StableAksVersionProviderRegistry allows runtime provider configuration (useful for testing).
• Comprehensive Testing: Added unit tests (80%+ coverage), integration tests, and functional tests.
• Documentation: Updated authoring guidelines with operator usage examples.

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The operator:

• Extracts location and properties.kubernetesVersion from AKS cluster resources.
• Normalises location names (lowercase, no spaces) for consistent matching.
• Fetches region-specific stable versions from Azure's AKS API (cached after first fetch).
• Returns true if the version stability matches the expected value in the rule.

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Example Usage

"path": "resources[*]",
  "where": {
    "path": "type",
    "equals": "Microsoft.ContainerService/managedClusters"
  },
"hasStableAKSVersion": true

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[RazvanLoghin1]

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