Opengraph/custom field

[shahzan01]

PR: Extend OpenGraph with Custom Field Mapping & Developer Interface

Description

This PR introduces custom field support for OpenGraph in the jacademy25_seo project.
It allows administrators to map Joomla custom fields into OpenGraph metadata and provides developers with a clear interface to make their custom fields OG-aware.

Key Features

1. Custom Field Mapping in Categories

   • Category edit form now includes an OpenGraph tab where admins can map custom fields to:
     • og:title
     • og:description
     • og:image
     • og:image:alt
   • Mapped custom fields become the source for OG metadata whenever menu or article overrides are not provided.

2. Built-In Grouping for Field Types

   • Custom fields can be grouped by their intended use:
     • TEXT → title, description
     • IMAGE → images for previews
     • IMAGE_ALT → alt text for accessibility and SEO

3. Developer Extension via OpenGraphMappableFieldInterface
   Developers can expose their custom fields to the OpenGraph system with minimal effort:

   • Step 1: Extend your field class with OpenGraphMappableFieldInterface.
   • Step 2: Implement the getOpengraphGroup() function.
   • Step 3: Return the correct group (TEXT, IMAGE, or IMAGE_ALT) depending on your field type.

   Example:

   class MyCustomField extends \Joomla\CMS\Field\TextField implements OpenGraphMappableFieldInterface
   {
       public function getOpengraphGroup(): string
       {
           return 'TEXT'; // or IMAGE / IMAGE_ALT
       }
   }