Add integration test support

[jgrandja]

We should provide an easy way to start up an Authorization Server instance for the purpose of running integration tests.

An integration test scenario will require the Authorization Server instance to be configured in such a way to meet the requirements of the test(s). Therefore, we need to provide a way for the Authorization Server instance to consume a custom configuration at startup.

***** UPDATE May 2, 2024 *****

Integration test support will be delivered in spring-boot-testjars. The project is currently in spring-projects-experimental and the plan is to eventually integrate into spring-boot.

See this branch for an example on how to start up a Spring Authorization Server instance for integration testing purposes. See this integration test as a starting point.