Error when referencing an unknown error_type: `body` is undefined

[AdamKing0126]

Original Issue

In https://github.com/department-of-veterans-affairs/vets-api/pull/15075 I logged the response.body in an attempt to assist further debugging efforts, but unfortunately body is not defined, and is now causing its own error.

This is because EVSS::GiBillStatus::GiBillStatusResponse does not expose the body of the response that is passed in as an initialization argument.

In order to determine the cause of these errors, modify the GiBillStatusResponse to include a body argument which is linked to the response.body