[DOC OCP] Incorrect container image user specified in AMQ Streams docs

Currently, the downstream container images are using a user "jboss" instead of the "strimzi" and "kafka" users specified in the upstream operator, bridge and Kafka images. However, in the downstream documentation [1] we reference the upstream "kafka" user in the line

USER kafka:kafka

when it should be:

USER jboss:jboss

[1] https://access.redhat.com/documentation/en-us/red_hat_amq/7.2/html-single/using_amq_streams_on_openshift_container_platform/index#using-kafka-connect-with-plug-ins-str