Add stub publishing_api_has_content
Add stub publishing_api_has_content

Eliminates duplication in functionality that previously occured between
publishing_api_has_fields_for_document_with_pagination and
publishing_api_has_fields_for_document methods.

publishing_api_has_content requires 2 arguments, items and
params={}, enabling flexibility in regards to number of args that
can be passed in to the params hash. This is now used in place of
publishing_api_has_fields_for_document_with_pagination and
publishing_api_has_fields_for_document.

alphagov/gds-api-adapters