Setup integration tests

Created by: rdgoite

I've added a new source directory where we can put integration tests for Ingest Core. I've also defined new Gradle tasks, integrationTest and verify that are used for running automated tests. integrationTest runs all tests in the integration directory, while verify runs all tests. Using SpringBootTest annotation on tests in integration source directory will now automatically setup an in-memory MongoDB instance that can be used for testing.

I've also added CI-related scripts for both GitLab and Github. As this PR would hopefully demonstrate, the Github workflow is programmed to run against PR's and merges to master.