[DOC OCP RHEL] Kafka Exporter changes for Streams 1.8

Add Kafka Exporter bug fixes to the Release Notes for AMQ Streams 1.8 (OCP and RHEL)

Add a known issue for KE: log levels can’t be changed from `INFO` level (OCP and RHEL)

There are NO documentation changes required for AMQ Streams on OpenShift. The new option (see below) is auto-enabled.

For AMQ Streams on RHEL, we need to document a new configuration option named:

--legacy.partitions

Only return metrics for active/connected partitions. If you want to return metrics for inactive partitions, enable the --legacy.partitions option.