Propagate datacite errors through API and GUI
Recently, a colleague got a doi from NOMAD that did not complete the registration process. At some point datacite answered with an standard overload message. This ended up in our logs, but we did not treat the error further. The DOI module has to report the error, the API has to propagate this error (i.e. HTTP 500 something), and the gui needs to display it. Further allow the user to repeat her request later.