feat: Add --override flag for plugin installation with --set support

[mrgb7]

Feature: Add --override flag for plugin installation

This PR implements the --override flag feature requested in #48, allowing users to force re-installation/update of plugins with custom configuration values.

🎯 What This PR Does

Adds support for forcing plugin re-installation with custom values:

playground cluster plugin add -n argocd --override \
  --set admin.password=newpass \
  --set server.replicas=3 \
  --set redis.enabled=true \
  --cluster playground

🔧 Key Features

• --override Flag: Forces re-installation even if plugin is already installed
• Multiple --set Flags: Support for multiple configuration overrides
• Nested Key Support: Dot notation for nested values (e.g., server.replicas=3)
• Type-Aware Parsing: Automatically parses strings, numbers, and booleans
• Plugin Validation: Each plugin validates allowed override keys
• Value Merging: Deep merges override values with plugin defaults

📝 Implementation Details

New Interfaces

• OverrideValidator: Validates override values per plugin
• OverridablePlugin: Allows plugins to accept override values

ArgoCD Plugin Support

• Validates allowed override keys (admin.password, server.replicas, etc.)
• Merges override values with default values from remote configuration
• Supports all major ArgoCD configuration parameters

CLI Enhancements

• Added --override boolean flag
• Added --set stringArray flag for multiple value overrides
• Robust parameter parsing with error handling

🧪 Testing

• ✅ Comprehensive unit tests for parameter parsing
• ✅ Tests for nested value handling
• ✅ ArgoCD plugin validation tests
• ✅ Value merging functionality tests
• ✅ All existing tests continue to pass

🎬 Usage Examples

# Override ArgoCD admin password
playground cluster plugin add -n argocd --override --set admin.password=newsecret --cluster dev

# Override multiple values
playground cluster plugin add -n argocd --override \
  --set admin.password=newsecret \
  --set server.replicas=3 \
  --set redis.enabled=true \
  --cluster production

# Override nested configuration
playground cluster plugin add -n argocd --override \
  --set server.resources.requests.memory=512Mi \
  --set server.resources.requests.cpu=200m \
  --cluster production

🔒 Safety Features

• Validation: Only allowed keys can be overridden per plugin
• Type Safety: Values are parsed and validated appropriately
• Error Handling: Clear error messages for invalid configurations
• Non-Breaking: Existing functionality remains unchanged

📋 Checklist

• --override flag implementation
• Multiple --set flag support
• Plugin interface extensions
• ArgoCD plugin override support
• Parameter parsing and validation
• Value merging with defaults
• Comprehensive test coverage
• Code formatting (go fmt)
• Linting compliance
• Documentation in CLI help

Closes #48