Context:
In the integration test code of the back-end we have a lot of code duplication, which is helper functions that allow us to interact with the Optimize rest-api. We should create dedicated client classes that help us to interact with the rest api, e.g. like how it's done with the AuthorizationTestHelper or the CollectionTestHelper.

AT:

• there is a utility client class for each Optimize endpoint
• the client classes are used in all integration tests
• the client classes are initialized in the AbstractIT, so we don't have to intialize them in every test class
• abstract classes that are just for the porpose of sharing those utility methods are being removed (e.g. possibly the AbstractAlertIT)