EPIC: Export - Create ExportContentletProcessor reusing existing export logic

Parent Issue

https://github.com/dotCMS/core/issues/29575

Task

We need to create a new ExportContentletProcessor that reuses the existing export logic from com.dotmarketing.portlets.contentlet.action.EditContentletAction while maintaining the current struts export functionality. This requires careful refactoring to ensure both the new job-based export and the existing export action work consistently. The processor should handle file storage, generate download links, and notify users upon completion.

Objectives

• Extract and centralize export logic from EditContentletAction
• Create new ExportContentletProcessor implementing job-based export
• Maintain backward compatibility with existing struct export functionality
• Ensure consistent export behavior across both implementations
• Implement secure file storage and download mechanism
• Integrate with dotCMS notification system

Technical Requirements

Code Refactoring

• Extract export logic from EditContentletAction into a shared service/utility
• Ensure the extracted logic handles all current export scenarios
• Maintain all existing export configurations and options

New Processor Implementation

• Create ExportContentletProcessor class
• Integrate shared export logic
• Add proper error handling and validation
• Implement progress tracking
• Add cancellation support
• Implement file storage mechanism
• Generate secure download links
• Integrate with notification system

Proposed Objective

Core Features

Proposed Priority

Priority 2 - Important
```[tasklist]

Tasks

• https://github.com/dotCMS/core/issues/30834
• https://github.com/dotCMS/core/issues/30837
• https://github.com/dotCMS/core/issues/30836
• https://github.com/dotCMS/core/issues/30835
• https://github.com/dotCMS/core/issues/30838
• https://github.com/dotCMS/core/issues/30839
  \`

Start with com.dotmarketing.portlets.contentlet.action.EditContentletAction and review the linked child issues 30834, 30837, 30836, 30835, and 30838-30839. Map the existing export behavior before assessing the ExportContentletProcessor work. Done means the shared logic supports both job-based and Struts exports, including storage, download links, progress, cancellation, errors, and notifications.