public void validate(Map<String, NewDocumentType> documentDefinitions,
                         Set<NewDocumentType> globallyDistributedDocuments) {
        verifyReferredDocumentsArePresent(documentDefinitions);
        verifyReferredDocumentsAreGlobal(documentDefinitions, globallyDistributedDocuments);
    }
Performs the following validations:
 - Verify that all global documents have required redundancy
 - Verify that all referred documents are present in services.xml
 - Verify that all referred documents are global

@author bjorncs
config-model/src/main/java/com/yahoo/vespa/model/content/GlobalDistributionValidator.java