Add create lifecycle CTA and order work item settings files

What does this MR do and why?

This MR does the following

1. separates the custom fields and custom status settings page code in different folders for readability and maintainability
2. Adds the create lifecycle CTA behind the new FF work_item_status_mvc2 which does not have anything else other than open/close modal for now

References

Screenshots or screen recordings

Before	After(with FF on)

How to set up and validate locally

1. Enable work_item_status_mvc2 FF
2. Go to issues settings page on group
3. See that you are able to see the create lifecycle button which just opens and closes the modal

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #556116 (closed)