PubSub deprecation - remove PubSub support, switch to Kafka

This story covers the second part of the "Phase 1 implementation plan" described in the PubSub deprecation plan.

• Remove all PubSub dependencies (mod-pubsub-client).

• Remove the MessagingDescriptor file.

• Remove endpoints that handle PubSub events from the ModuleDescriptor (that's a breaking change!).

• Remove all the code that registers or unregisters a module as a publisher or a subscriber of PubSub event types. Most likely, this code will be a part of the _tenant API. Replace it with the code that creates Kafka topics using KafkaAdminClientService. 

• Replace the code that publishes PubSub events with Kafka message producing.

• Replace the code that consumes PubSub events with Kafka message consuming.

In scope:

• PubSub functionality removal

• Producing and consuming Kafka messages

Note: All functionality that depends on PubSub may be affected, including: patron blocks, circulation logs, loans being closed based on fee/fine payments.
Note: This is a breaking change.