It has been proposed to apply :

db.adminCommand({setParameter: 1, wiredTigerEngineRuntimeConfig: "file_manager (close_idle_time=30,close_scan_interval=30,close_handle_minimum=100)" })

If you run lets say 100 clusters of MongoDB Servers/Operators then it is not a viable option to apply 100x the command above.

Please make this config item and others also available as a configurable parameter.