Add "UK and the Commonwealth" international delegation.

A data migration to add the new international delegation.

Ticket: https://www.agileplannerapp.com/boards/173808/cards/8993
Merge pull request #1923 from alphagov/add_uk_and_commonwealth_delegation

Add "UK and the Commonwealth" international delegation.
Don't publish non-case-study unpublishings.
Merge pull request #1924 from alphagov/only-case-study-unpublishings

Don't publish non-case-study unpublishings.