Extract pages_domain_presenter into a helper fixing related bugs

What does this MR do?

In #30146 (closed) we introduced PagesDomainPresenter and a few bugs related to this change.

This MR fixes 2 bugs:

• if there are validation errors on creation, presenter wasn't used this caused an error while rendering #216728 (closed)
• verify button wasn't working properly #215632 (closed)

Alternative solution:

1. Add .present(current_user: current_user) in create method
2. Use @domain.pages_domain or @domain.subject in verify method

I tried it, but it looks like adding a lot of workarounds for the problem which could be avoided.

We don't use helper_method in gitlab codebase much, but it looks suitable here.

I'm open to other suggestions, but I want to keep domain and domain_presenter separate.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team