Even though the requiresSearchSequenceToken field is optional for users, we don't use the InternalSearchMongotRemoteSpec to validate parsing of $search. That means we can make requiresSearchSequenceToken non-optional in the spec, with a default value of false, if un-provided. This way we can avoid having the default "false" scattered a few times like "_spec.getRequriesSearchSequenceToken().get_value_or(false)"