[Improvement]: Improve generic error message when importing an existing config.

[mattamon]

Improvement description

Version: Latest version of datahub

When trying to import an existing config into the datahub a generic error message will show up instead of showing the actual error.

The actual error is visible in the browser console.

It would be better not to have the error in the console, but rather show it in the error popup.

It is even a 500er error which should not happen at this point since it is getting validated.

[github-actions]

Thanks a lot for reporting the issue. We did not consider the issue as "Pimcore:Priority", "Pimcore:ToDo" or "Pimcore:Backlog", so we're not going to work on that anytime soon. Please create a pull request to fix the issue if this is a bug report. We'll then review it as quickly as possible. If you're interested in contributing a feature, please contact us first here before creating a pull request. We'll then decide whether we'd accept it or not. Thanks for your understanding.