Add ability to choose registration form redirect from settings

Problem/Motivation

My client would like to redirect to the event page after registration. https://www.drupal.org/project/recurring_events/issues/3302916 → hard-coded the registration form redirect to go to the current page. I feel a more flexible solution is to allow a choice under Registration Settings so site builders can do what they wish.

Steps to reproduce

Register for an event and form will reload the same page after registering.

Proposed resolution

Add settings to allow site builders to choose where the registration form redirects. Choices could be current page (default), event instance page, event series page, or a custom URL.