[2.x] Move email_registration settings in its own fieldset

Starting with this now!

Here we go, works for me! Please review!

@LRWebks: Nice! Here comes the trap: Changing form structure may lead to broken validation / submit logic (that's based on the #tree property on form arrays). If it is a tree, you may need to also adjust the handling logic. Same may happen for configs!

So please try, if it still works as expected. Don't rely on test coverage for modules and please provide information if and how much you tested, when setting an issue to "Needs review", please. So we're informed how safe it is and if it needs further (manual or automated) testing. Welcome to the next level :P

As far as I have searched through the code, all classes that use these settings get them directly from the configFactory via $container->get('config.factory')->get('email_registration.settings'), the previous fieldset that they were in was never mentioned anywhere, so I guess the fieldset doesn't matter if it is done this way?
I see no need to change anything - manual tests work, automated tests work...

@Grevil: Please review then :)

LGTM! Sry, I said "fieldset", but I meant "details" wrapper. Small adjustments, everything else is perfect!

Automatically closed - issue fixed for 2 weeks with no activity.