Add entities to a case

Add companies and people to an existing case

This behaves the same as the Create Case endpoint when adding companies or people.

When adding companies, it is possible to retrieve company registration data. To do this registry_search must be set to true, and company_name, company_number and jurisdiction_code must not be empty.

If the data cannot be found, then the case is created with the company details provided.
When the company is found, then the status, number_of_officers and number_of_owners are updated to reflect the registry data.

Optionally, it possible to add all the company's officers (the human ones) to the case by setting add_directors to true. This flag only applies if registry_search is true.