feat: add --config/-C flag to deploy command for custom configuration files

[themmyloluwaa]

🎯 What this PR does

Adds support for custom deployment configuration files via the --config/-C flag in the pcc deploy command.

🚀 Usage

# Use custom config file
pcc deploy --config /path/to/custom-config.toml

# Short flag version  
pcc deploy -C ./staging-config.toml

# Override config values with CLI args
pcc deploy --config base-config.toml my-agent custom-image:v2

🔧 Technical Changes

• CLI: Added --config/-C parameter to deploy command
• Config Loading: Enhanced load_deploy_config_file() to accept custom paths
• Decorator: Updated @with_deploy_config to handle custom config paths
• Backward Compatibility: Existing pcc deploy commands continue working unchanged

✅ Testing

• Added comprehensive test suite (7 tests) covering:
  • Custom config file loading
  • Error handling for invalid/missing files
  • Decorator integration
  • Backward compatibility
  • Default fallback behavior

🎯 Why this change?

Users previously could only use pcc-deploy.toml in the current directory. This enhancement enables:

• Environment-specific configs: Different configs for dev/staging/prod
• Shared configs: Reusable configuration files across projects
• Organized workflows: Keep configs in dedicated directories

🔒 Backward Compatibility

✅ No breaking changes - existing workflows continue working exactly as before.

📝 Additional Notes

• Flag conflicts resolved: Used -C (capital) to avoid conflicts with existing -c (credentials) and -f (force) flags
• Error handling: Graceful handling of missing files, invalid TOML, etc.
• CLI precedence: CLI arguments still override config file values as expected