Add Worldwide Corporate Information Page content item

Currently, the corporate information pages associated with worldwide
organisations are published as `placeholder` content items.

This creates a new content item for them.

The existing content item for corpoarate information pages could be used
instead. However:
- We require a link to the associated `worldwide_organisation`. Having a new
  content item means that we don't have to attach multiple optional links to the
  corporate information page content item.
- We will need a new template for this page in `government-frontend` as the
  worldwide organisation corporate information pages are quite different when
  compared to the organisation corporate information pages. Because
  `government_frontend` maps content items to templates through their
  `schema_name` (except for a few exceptions), it would make sense to follow this
  pattern.
- Many of the attributes of the corporate information page schema are not
  needed in order to render the worldwide organisation corporate informaiton pages.