I am new to snowplow and I'm having a problem where I want to use a value in the enriched data, a user id, as the key for a key-value message when Snowplow sinks to Kafka. Right now, for each message Snowplow sinks to Kafka, the key is a uniquely generated string and the value is a tab separated string. However, I want the key to be the user id, the (nth) column in the value, so that I know that each user's data will go to the same partition every single time. Is there any way I can choose the value of the key? If not, are there any other ways I could solve this problem? Any help would be great.