The WiredTigerConfig is a parameter-pack that is supposed to simplify construction of kv engines. However we have recently started making configs runtime-settable, which poses thread-safety concerns in having them stored (redundantly) both in atomic server parameters and in the wt configs.

These parameters just shouldn't be part of the wt config and we need a more dynamic-dispatch approach to choosing different configs for spill vs regular engines.

Specifically `wiredTigerEvictionThreadsMax` and `...Min` are problem cases