Add AKS (Azure Kubernetes Service) support

[Copilot]

This PR adds comprehensive support for Azure AKS clusters to kdiscover, addressing issue #XX.

What's Added

New Commands

• kubectl discover aks list --azure-subscriptions <subscription-id> - List AKS clusters across Azure subscriptions
• kubectl discover aks update --azure-subscriptions <subscription-id> - Update kubeconfig with AKS cluster credentials

Key Features

• Multi-subscription support: Discover clusters across multiple Azure subscriptions using comma-separated subscription IDs
• Azure authentication: Uses Azure's default credential chain (Azure CLI, managed identity, environment variables, etc.)
• Consistent UX: Same command patterns, table output format, and error handling as existing AWS EKS support
• Robust error handling: Clear error messages for missing subscriptions, authentication failures, and other common issues

Implementation Details

The implementation follows the same architectural patterns as the existing AWS support:

• Azure SDK integration: Uses official Azure SDK for Go to discover and manage AKS clusters
• Authentication: Leverages kubelogin for AKS cluster authentication in generated kubeconfig
• Concurrent discovery: Parallel cluster discovery across multiple subscriptions for performance
• Backup functionality: Automatically backs up existing kubeconfig before updates

Examples

List AKS clusters

kubectl discover aks list --azure-subscriptions subscription-id-123
┌────────────────────────────────────────────────────────────────────────────────┐
│     cluster name                  region              status  exported locally │
├────────────────────────────────────────────────────────────────────────────────┤
│  1  production-aks                eastus              Succeeded       No       │
│  2  staging-aks                   westus2             Succeeded       No       │
│  3  dev-aks                       centralus           Succeeded       No       │
├────────────────────────────────────────────────────────────────────────────────┤
│                                   number of clusters  3                        │
└────────────────────────────────────────────────────────────────────────────────┘

Update kubeconfig with AKS clusters

kubectl discover aks update --azure-subscriptions subscription-id-123
Update all AKS Clusters
Found 3 clusters remote
Backup kubeconfig to /Users/user/.kube/config.bak
Updated kubeconfig at /Users/user/.kube/config

Testing

• Comprehensive unit tests for Azure package functionality
• Integration tests for cluster discovery and kubeconfig management
• Manual testing with dummy subscriptions validates error handling
• All existing tests continue to pass

Breaking Changes

None. This is a purely additive change that doesn't affect existing AWS functionality.

Documentation

• Updated README.md with AKS examples and feature description
• Updated help text to reflect multi-cloud support
• Added inline documentation for all new functions

Original prompt

---

This section details on the original issue you should resolve

<issue_title>add AKS support </issue_title>
<issue_description>Is your feature request related to a problem? Please describe.
AKS has a good share of cloud usage.

Describe the solution you'd like
kubectl discover aks ...

</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #42

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