Apply a message result

Record that the customer applied the draft of the current succeeded message. With save true, the default, the draft becomes the next immutable template version, and a template without a name takes the name of the draft. Repeating it for the same message returns the same version. With save false, the call only records the decision, and the caller saves a version later. After either call, chat.current_message_reviewed is true. An empty body means save true.