Add integration tests

[myNameIsPatrick]

Description

As a developer, I want to be able to run integration tests against the hop client to validate the client's correctness to handle various types of messages through a running Kafka broker.

Definition of Done

• Add pytest-style integration tests with marked as 'integration' with sufficient coverage
• Add in an extra Makefile target which runs the full test suite (unit + integration) alongside unit tests only (no integration)
• Modify the CI pipeline so that only unit tests run on every commit
• Modify the CI pipeline so that integration tests run only when triggered or during an initial PR
• Modify the CI pipeline so that a Kafka broker gets spun up for the integration testing stage