Pub/sub client: Subscribers.post permission required when no subscribers

The pubsub.subscribers.post permission is required when I use org.folio.util.pubsub.PubSubClientUtils#registerModule method to register my module even though no subscribers present in the MessagingDescriptor.json at all.

Steps to repro:

1. Create a messaging descriptor with either no subscriptions property or empty:

   {
     "publications": [
       {
         "eventType": "DI_FEESFINES_ACCOUNT_WITH_LOAN_CLOSED",
         "description": "An account with a loan associated is closed",
         "eventTTL": 30,
         "signed": false
       }
     ]
   }
   

2. Attempt to register a module using the descriptor by calling org.folio.util.pubsub.PubSubClientUtils#registerModule method.

Expected:

The module is deployed and registered as publisher.

Actual

The registration process failed with following exception:

org.folio.util.pubsub.exceptions.ModuleRegistrationException: 
Module's subscribers were not registered in PubSub. HTTP status: 403

Dev notes:

There is a check descriptorHolder.getSubscriberDescriptor() != null in the method to decide whether to execute API call to pub/sub or not. It seems that getSubscriberDescriptor() always returns non-null value. The check have to be modified to descriptorHolder.getSubscriberDescriptor().size() > 0.

Similar issue should happen with publications property.