Ticket/12783 Move require:phpbb/phpbb to extra:phpbb/phpbb in Extensions composer.json files

Alternative2: #2683

https://tracker.phpbb.com/browse/PHPBB3-12783
Can we make this `['extra']['soft-require']['phpbb/phpbb']` as then it's explicitly stated it's still a requirement/dependency but it's soft as it won't prevent installation etc.