Changes to List provider types the gateway can construct, with their credential forms

added the new internal_error enum value to the type response property for the response status 401

added the new internal_error enum value to the type response property for the response status 503

added the new permission_error enum value to the type response property for the response status 401

added the new permission_error enum value to the type response property for the response status 503

the items response's property type changed from string to object for status 200

added the optional property items/default_base_url to the response with the 200 status

added the optional property items/fields to the response with the 200 status

added the optional property items/type to the response with the 200 status

endpoint added