Add staging mode configuration to deployment settings

[Soner (shyim)]

Summary

This PR adds support for staging mode configuration in the deployment settings, allowing users to control whether staging setup commands are executed during installation and upgrade processes.

Key Changes

• Added ConfigDeploymentStaging struct to internal/shop/config.go with an Enabled boolean field to control staging setup command execution
• Extended ConfigDeployment struct to include an optional Staging field referencing the new staging configuration
• Updated the JSON schema (shopware-project-schema.json) to include the new ConfigDeploymentStaging definition with proper type and description
• Added staging property to the deployment configuration schema
• Minor documentation improvement: removed "locally" from asset caching description for clarity

Implementation Details

• The Staging field is optional (uses omitempty tag) to maintain backward compatibility
• The staging configuration is defined as a separate struct for better organization and potential future extensibility
• Both the Go code and JSON schema have been updated consistently with matching descriptions

https://claude.ai/code/session_01CHUaF3xNhgHWHbj13KetiD