Add global filter to customize table structure resolution

[phschmanau]

What does this Pull Request do?

This Pull Request introduces a new catch-all filter that allows developers to modify or fully replace the resolved table structure for any WordPress object type inside get_wordpress_table_structure().
This makes it possible to support custom taxonomies (and optional custom post types) without modifying the plugin code directly.

Previously, only a hard-coded set of taxonomy slugs (category, tag, post_tag) was supported.
With this PR, developers can hook into the new filter and return their own table structure for any custom taxonomy or object type while maintaining full backward compatibility.
The plugin’s default behavior remains unchanged if no filter is used.

How do I test this Pull Request?

1. Ensure that at least one custom taxonomy is registered (e.g. via a theme, plugin, or simple test snippet).
   This is required so the filter can override its table structure.
2. Register a filter for object_sync_for_salesforce_wordpress_table_structure in a theme, plugin, or mu-plugin.
3. Inside the filter callback, return a custom table structure for the registered taxonomy slug (e.g. region or canton).
4. Trigger any plugin functionality that calls get_wordpress_table_structure() with that taxonomy.

Example: Overriding table structure for a custom taxonomy

add_filter( 'object_sync_for_salesforce_wordpress_table_structure', function( $structure, $object_type ) {

    // Custom taxonomies we want to treat like WP terms.
    $custom_taxonomies = [ 'region', 'canton', 'district', 'municipality' ];

    if ( ! in_array( $object_type, $custom_taxonomies, true ) ) {
        return $structure;
    }

    global $wpdb;

    return [
        'object_name'     => 'term',
        'content_methods' => [
            'create' => 'wp_insert_term',
            'read'   => 'get_term_by',
            'update' => 'wp_update_term',
            'delete' => 'wp_delete_term',
            'match'  => 'get_term_by',
        ],
        'meta_methods'    => [
            'create' => 'add_term_meta',
            'read'   => 'get_term_meta',
            'update' => 'update_term_meta',
            'delete' => 'delete_metadata',
            'match'  => 'WP_Term_Query',
        ],
        'content_table'   => $wpdb->prefix . 'terms',
        'id_field'        => 'term_id',
        'meta_table'      => [
            $wpdb->prefix . 'termmeta',
            $wpdb->prefix . 'term_taxonomy',
        ],
        'meta_join_field' => 'term_id',
        'where'           => '',
        'ignore_keys'     => [],
    ];
}, 10, 2 );