v3.9.0

• New: Updated sabre/xml library to version 4.
• New: Added notice about dropping support for PHP versions below 7.4.
• New: Implemented PSR-4 Autoloading Standard for improved code structure and maintainability.
• New: Deprecated wpo_wcpdf_due_date_display hook.
• Fix: WC item meta style issue when using dd.
• Fix: Relocated wpo_wcpdf_use_path hook before $src empty check.
• Translations: Updated translation template (POT).