[SPIKE] Provide interface for testing logic that gets invoked via UMB messages

As a QE, I want to be able to test the partner contract creation logic without injecting messages onto UMB. 

There are three ways that logic can be invoked in swatch.  Rest API, kafka messages, or UMB messages.  Today, IQE supports Rest API & Kafka, but not UMB.  swatch-contracts consumes UMB messages from entitlement gateway.  We don't want to have to inject UMB messages for testing purposes in a stage/prod environment, so we want to provide a different interface.

During dev sync on 4/17, we discussed a couple different options to try out.
Camel
https://camel.apache.org/camel-quarkus/next/reference/extensions/rest.html
https://stackoverflow.com/questions/18691066/camel-routing-on-when-header-value 
 
Smallrye
https://quarkus.io/guides/kafka-reactive-getting-started 
https://github.com/RedHatInsights/rhsm-subscriptions/pull/2051/files#diff-ab17e4a64cb7fef85b50ef32f965ffc4f271b476792278eeb54c8d919654d9b2R131 

• we could listen to UMB and kafka topics in stage

Done

• Working POC using quarkus smallrye messaging or quarkus camel/restapi that will allow IQE tests to to invoke the application logic for creating a contract