Modify keyvalue kafka log entry to include keyvalue text/value being posted

[umayaml]

In order to update Neurons in Neuprint for status and name, keyvalue datatype needs to post the value being kvpost in the Kafka logs. That way, we don't need to contact DVID to get the changes made to status and name for the Neurons. I think this should probably be an option when creating the keyvalue since it only really applies to keyvalues that store text (example segmentation_annotations). An alternative solution is to create a new type of keyvalue that only allows text and limits the size. This new keyvalue type will log the existing text, text posted and deleted to the keyvalue in kafka.