Use ProblemDetails

With KAFE finally safely resting in its new home, mlejnek on Stratus.FI, I finally have time to work directly on KAFE.

I bumped into a bug with the TemporaryAccountClosed event. Marten had no knowledge of it, yet it was in the database. This happened because, I removed the event type from the C# codebase back in December. The fix was simple enough: I added an upcaster from TemporaryAccountClosed to TemporaryAccountRefreshed.

However, there was also an issue with the app not logging the error, so I had to take a look at ASP.NET Core's error handling. Based on that, I realized that the JSON that ASP.NET Core returns is actually standardized as RFC 7807. So now we use Microsoft.AspNetCore.Mvc.ProblemDetails and log the error as well.