fix: datadog metrics should provide http status code on error if non-2xx response

[erikmiller-gusto]

currently the log line exposes the error, however that's always going to be nil based on the check just above it. This provides better visibility into the failure reason

Previously:

frontend-errors-beta: error response: : %!w(<nil>)

Now:

frontend-errors-beta: error response: : 500 InternalServerError