Feature: #95808 - Enable item groups from foreign tables 

Description 

A new TCA option foreign_table_item_group has been introduced for the TCA types select and category. It allows extension authors to define a specific field in the foreign table, holding an item group identifier. As described in the TCA reference, this needs to be a string.

Therefore, it's now possible to also use the item groups feature, introduced with forge#91008, for TCA columns with a foreign table lookup.

Example 

'select_field' => [
    'label' => 'select_field',
    'config' => [
        'type' => 'select',
        'renderType' => 'selectSingle',
        'items' => [
            ['label' => 'static item 1', 'value' => 'static-1', 'group' => 'group1'],
        ],
        'itemGroups' => [
            'group1' => 'Group 1 with items',
            'group2' => 'Group 2 from foreign table',
        ],
        'foreign_table' => 'tx_extension_foreign_table',
        'foreign_table_item_group' => 'itemgroup'
    ],
],

In case the foreign_table_item_group field of a foreign record contains an item group identifier, not set in the local itemGroups configuration, the database value will be used as label in the select box, as it's also the case for static items with a group set to a value, which is not configured in itemGroups.

Impact 

Using the new foreign_table_item_group TCA config option, it's now possible to use the items group feature even for items from foreign tables.