Split test suite into independent unit/integration suites

[jaden-young]

Currently a sizable portion of the plugin's test suite relies on/intends to test Spring Boot's initalization, which fails without successfully connecting to a RabbitMQ broker. Most notably, this makes CI builds constantly fail. We want to be able to test as much as we can locally without requiring a running broker, and we also want CI to be able to run the full test suite.

The project's tests should be segmented into indepdenently runnable unit and integration suites, both of which should be run during a CI build.