Feature: #92423 - Enable placeholder config for ckeditor

See forge#92423

Description

After the update of ckeditor to version 4.15.0, a new ckeditor plugin, called Editor Placeholder, is now available. More information along with an example can be found in the official documentation.

The placeholder configuration of TCA type text is now fed into the ckeditor plugin:

'bodytext' => [
    'label' => 'LLL:EXT:core/Resources/Private/Language/locallang_general.xlf:LGL.text',
    'config' => [
        'placeholder' => 'This is a placeholder',
        'type' => 'text',
        'enableRichtext' => true,
    ]
]

Impact

Editors can now be supported by providing a placeholder text also for the ckeditor.