Implement Remove-AzBootstrapEnvironment function with comprehensive cleanup and interactive mode

[Copilot]

This PR implements the Remove-AzBootstrapEnvironment function to provide complete environment removal capabilities, addressing the functionality that was previously removed when focusing on Bicep-based resource creation.

Changes

New Functions Added

• Remove-AzBootstrapEnvironment (public) - Main orchestrator function with both parameter-based and interactive modes
• Get-AzBootstrapEnvironmentConfig (private) - Reads environment configuration from .azbootstrap.jsonc tracking file
• Remove-GitHubEnvironment (private) - Deletes GitHub environments via GitHub API
• Remove-AzDeploymentStack (private) - Removes Azure deployment stacks with automatic resource cleanup
• Remove-AzBootstrapConfig (private) - Updates configuration file to remove environment entries

Key Features

Interactive Mode: When no environment name is provided, the function displays available environments from the tracking file and allows selection by number or name:

# Interactive mode - shows list of environments to choose from
Remove-AzBootstrapEnvironment

Parameter-based Mode: Direct specification of environment and repository details:

# Remove specific environment
Remove-AzBootstrapEnvironment -EnvironmentName "test" -Force

# With explicit repository details
Remove-AzBootstrapEnvironment -EnvironmentName "prod" -GitHubOwner "myorg" -GitHubRepo "myrepo" -Force

Comprehensive Cleanup: The function removes:

• Azure deployment stack (automatically deletes resource group, managed identities, role assignments, etc.)
• GitHub environments (both plan and apply environments)
• Environment entry from .azbootstrap.jsonc tracking file

Robust Error Handling: Continues cleanup operations even if individual steps fail, ensuring maximum resource cleanup with appropriate warnings.

Implementation Details

• Leverages the .azbootstrap.jsonc tracking file introduced in Add .azbootstrap.jsonc tracking file to monitor resources under az-bootstrap control #32 to identify managed resources
• Uses Azure deployment stacks for clean resource removal (consistent with creation pattern)
• Follows existing code patterns from Add-AzBootstrapEnvironment for consistency
• Implements idempotent operations that handle missing resources gracefully
• Supports WhatIf and Confirm parameters for safe operation

Testing

Added comprehensive test coverage with 13 new tests:

• Test-GetAzBootstrapEnvironmentConfig.Tests.ps1 - Configuration file reading
• Test-RemoveGitHubEnvironment.Tests.ps1 - GitHub environment deletion
• Test-RemoveAzBootstrapConfig.Tests.ps1 - Configuration file updates
• Test-RemoveAzBootstrapEnvironment.Tests.ps1 - Main function integration

All existing tests continue to pass, ensuring no regressions.

Documentation

Updated README.md with:

• Usage examples for environment removal
• Detailed explanation of cleanup operations
• Interactive mode documentation

Usage Examples

# Interactive mode
Remove-AzBootstrapEnvironment

# Remove specific environment with confirmation
Remove-AzBootstrapEnvironment -EnvironmentName "test"

# Force removal without prompts (for automation)
Remove-AzBootstrapEnvironment -EnvironmentName "staging" -Force

The implementation provides a clean, user-friendly way to remove environments while ensuring thorough cleanup of both Azure and GitHub resources.

Fixes #16.

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