The API helper `render_api_error!` previously would log a 400 error with
no details in `api_json.log`, which made it difficult to debug problems
in production. To fix this, we:

1. Store the intended status code in the request
environment. grape-logging doesn't pass this along to the loggers:
https://github.com/aserafin/grape_logging/issues/71

2. In the logger, check the code. If it is 400, attach an `api_error`
field that contains the response from the server.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/214879