Currently, it is not possible to group Content Type Fields as it was in eZ Publish platforms. Although the Select box is available in Content Type definition page, it has no choice values.

Steps to reproduce

• create a new content Type
• add a new fieldDefinition
• verify that Field Group selection box presents no choices.

In eZ Publish, the choice list was populated in legacy settings
https://github.com/ezsystems/ezpublish-legacy/blob/master/settings/content.ini#L262

In eZ Platform, the choice definition is blanked in
https://github.com/ezsystems/repository-forms/blob/master/lib/Form/Type/FieldDefinition/FieldDefinitionType.php#L72