Expose errors on failed imports for Bitbucket Server/Cloud importer
When project import fails using Bitbucket/Github/Gitea importers the project state is Failed
without any indication on why it failed. This makes customers to log a new issue, support + product engineers to investigate it, search logs, etc to tell what went wrong.
Instead, we could expose error message on importer projects page so that there is something actionable for customer straightaway.