v5.0.0

Removes the AssembliesToScanForValidators option as since 4.1.0 it was no longer necessary and it's usage now was confusing to describe (e.g. if supplied, you still need to register the validators with DI).

It's only remaining purpose was to "filter out" validators from non-included assemblies so FairyBread wouldn't use them in it's pipeline, but I doubt anyone was using it for that purpose and that wouldn't improve perf.

If anyone does want filtering, we could look to introduce that under a new option.