Make a string which has a valid JSON format to be parsed by the workflow engine

See attachment.

A custom function/integration might return a String with a valid JSON payload, but not being a strict JsonNode java object.

Mainly on use cases in which the user has no Java environment or tools that can unmarshal a JSON payload to Jackson's JsonNode, the workflow engine should be able to understand that a String can contain a valid JSON payload.

No matter its contents, a String is currently returning a TextNode.