Refactor Header Component

[willcAND]

Currently, the header component is overly complex and includes examples such as example-header-external-with-sub-navigation which are using a subNavigation object parameter not documented inside the navigation inside header/_macro-options.md.

Additionally, the header component is allowing for text or title to be passed into the itemsList array for navigation links. This change was made here - #1826 to avoid a Breaking Change. Needs to be updated to title only.

header is also using the navigation component which is not documented on the site, so it should be refactored to use thesection-navigation component instead.