Update to show Wagtail menu title field in menu if it exists

[patphongs]

Summary

What we're after:
Currently, the Wagtail menu no longer utilizes the menu title field when it's published. The menu title should no longer be required, but we should bring back the menu title within the Wagtail page view if it's present. If it's not present, it should retain the draft title or published title from the content tab.

Menu title field

Desired state if menu title exists after publish

Desired state if menu title DOES NOT exists after publish

Related issues

List any relevant related issue(s)

• Wagtail wish list: Copied Wagtail draft page should use new page title in the menu #4416
• Show title for copied pages in draft #4785

Completion criteria

• Menu title appears if it exists after publish
• Make menu title not required