fix(Apps): add error detail when exporting app config

[gortiz-dotcms]

Problem

A generic message was displayed when getting an error in the Apps export config tab. Also, it wasn't considering the case when the API that was requesting returned an error.

Fix

Added a check that validates if the response has an error-message as headers (this means that the API is returning an error) and if its has, then throw an error so it can be received correctly, and when received, display it.