Problem/Motivation
The pager by default uses an h4, this creates the `Heading levels should only increase by one` error in many use cases.
Steps to reproduce
Create a view with a pager that has no other content on the page.
Run axe devtools
Proposed resolution
Add ability to set the heading level per view pager.
Options should be h1 - h6
Remaining tasks
Create MR
Accessibility review - major objection from accessibility maintainer in comment #30
Replace static h4 with dynamic value in all themes
Add update hook to add views.settings for pager heading
Add descriptive text describing when to change heading level
Add tests
