[DOC RHEL] Add ZK scale-up/down procedures to Streams 1.4 Release Notes

Strimzi PR#2637 contains new procedures for manually scaling ZooKeeper clusters after upgrading to AMQ Streams 1.4. See https://github.com/strimzi/strimzi-kafka-operator/pull/2637

We need to include these procedures in the AMQ Streams 1.4 on RHEL Release Notes.

For Streams on RHEL only, the procedures must include the "Settings Changes" described in the draft doc. Notes from Tom Cooper:

For Streams on RHEL the user will need add:
standaloneEnabled=false
reconfigEnabled=True
to their settings
However they will need to log into their ZK cluster using whatever method they use to authenticate against it and run the reconfig commands in the proceedure
however I am not clear on how far we need to go on documenting this
There is already stuff on auth ZK in there so I think it is ok to say the user should auth using the method they have chosen and then run the reconfig add/remove commands
Maybe a note saying that if they are not using auth (not recommended) then they might need to restart their ZK servers with the -Dzookeeper.skipACL=yes java system property

Also, increment the supported ZK version to 3.5.7