orderedBeforeGenerators and orderedAfterGenerators without ignoreGenerators cause loader to crash

In [ConfigurationValidation.java:68-75](https://github.com/typedb-osi/typedb-loader/blob/master/src/main/java/config/ConfigurationValidation.java#L68-L75) `getIgnoreGenerators()` is called when it may be null, which causes the loader to crash if the orderedBeforeGenerators or orderedAfterGenerators were defined, but ignoreGenerators weren't.