Added the posibility to configure the JsonSerializer to serialize enums as strings

Now you can configure the JsonSerializer to serialize enums as its string representation.

    var bus = Configure.With(adapter)
    ...
    .Serialization(s => s.UseJsonSerializer().SerializeEnumAsStrings(false))
    ...
    .CreateBus();

I think that is usefull when troubleshooting, as you don´t have to make the "mental translation" between the enum representation and its value.