[DOC OCP] Kafka's default heap size (-Xmx) should be 22% of the memory request

• Kafka's default heap size (-Xmx) should be 22% of the memory request
• In our documentation, "Use a memory request that is at least 4.5 × the -Xmx"(1).
• 22% == 1 / 4.5
• However, in the current implementation, its defaults is 50%.

(1) https://access.redhat.com/documentation/en-us/red_hat_amq_streams/2.0/html-single/using_amq_streams_on_openshift/index#con-common-configuration-jvm-reference