Consider not including fields in default Workflow serialization

[frankbuckley]

When using Workflow, the default JSON serializer is configured to include fields by default.

public class JsonDataConverter : DataConverter
{
    // WARNING: Changing default serialization options could potentially be breaking for in-flight orchestrations.
    static readonly JsonSerializerOptions DefaultOptions = new()
    {
        IncludeFields = true,
    };

This is unusual as it is not the default in .NET and might lead to unexpected data leaks/disclosure.

Changing the default is a breaking change for existing workflows, but it seems unlikely that users are relying on this unusual behaviour. If anyone is then the configuration can be overridden.