setClusterParameter and getClusterParameter are gated behind FCV 6.0, as implemented in SERVER-62266. As new cluster server parameters are introduced to the server for FCV > 6.0, we will need a finer way of ensuring that specific parameters are restricted from being set after downgrade even as the commands themselves remain available. 

Add a minimum FCV IDL option to server parameters. When set, if the FCV currently known to the server (note: mongos is unaware of the FCV, so this does not apply) is less than the set minimum FCV, the parameter will be disabled, and setParameter and getParameter will fail.

For cluster server parameters, upon FCV downgrade, if the new FCV is less than the set minimum FCV, the parameter's value will be deleted from storage. Also, while getClusterParameter will still succeed on mongos if the cluster's FCV is less than the minimum FCV, setClusterParameter will fail in this case.