Provide JsonSerializerSettings customization for EntityFramework provider

[martikyan]

Is your feature request related to a problem? Please describe. There is a use case where we need specific JsonSerializerSettings for the EntityFramework provider's ExtensionMethods. However, the settings are not exposed and, therefore, cannot be customized.

Describe the solution you'd like I would like WorkflowOptions to have a method that allows modifying settings for the serializer.

Related: #231