[WebClientDAT] Content Type application/json encoding

It would be really nice if the webClientDAT would get the abbility to choose how the data dictionary is encoded. It seems like the standart for aht now is application/x-www-form-urlencoded, which some APIs do not like, esp when working with GraphQL.
i can implement it by setting the contenttype in the header dict and converting the dictionary to json string using dumps by hand. More for convinience :slight_smile: