FindKeyBy value constraint should be relaxed to any

[powerman]

Real use case: map of maps. When map's value type is another map it is not comparable, but this isn't required to run predicate function.

Example:

var m map[K1]map[K2]V2
_, found := lo.FindKeyBy(m, func(k1 K1, v1 map[K2]V2) bool {
	_, found := lo.FindKeyBy(v1, func(k2 K2, v2 V2) bool {
		return match(v2)
	})
	return found
})