Sources jars are missing in Maven repository

Sources jar are missing from maven repo which makes it hard to debug or quick look at the source code inside the IDE where sources for given version can be downloaded with one click. Whereas now one has to go and clone the github repo and attach sources manually.

example:
http://packages.confluent.io/maven/io/confluent/kafka-avro-serializer/5.2.1/kafka-avro-serializer-5.2.1.jar <- works great
http://packages.confluent.io/maven/io/confluent/kafka-avro-serializer/5.2.1/kafka-avro-serializer-5.2.1-sources.jar <- doesn't 😞

Start by reproducing the two Maven repository URLs in the issue for kafka-avro-serializer 5.2.1, then inspect this repository's Maven publishing or release configuration; no specific files or tests are named. Done means the corresponding -sources.jar is published and downloadable for the affected artifacts and versions.

Written by the indexing model from the issue text.