Change default exception details property name
Change default exception details property name

Fixes #102

Exception details share the same JSON property name `"errors"` as validation errors, except as an array instead of a JSON object.
This causes problems with libraries like [Refit](https://github.com/reactiveui/refit), where it no longer is able to deserialize the `ProblemDetails` object and throws an `Refit.ApiException` instead of `Refit.ValidationApiException`.

Exception details is enabled when running in `Development` environment, by default.

### Changes
- Change `DefaultExceptionDetailsPropertyName` from `errors` to `exceptionDetails`
 
### Testing
- Refit throws `Refit.ValidationApiException` and is able to deserialize the `ProblemDetails` object.
khellang/Middleware,khellang/Middleware