Important: #85689 - Replaced default value with placeholder in external url link handler

Description

The UrlLinkHandler in EXT:recordlist used a default input value "http://" for external links. This is not practical because editors often paste a link in the field. This caused broken links due to duplicate HTTP protocols, for example: http://https://typo3.org/

A placeholder is now used instead of a default value. Editors can paste links directly and do not have to remove a default value first.