[EPIC] Steering API integration test suite (high prio endpoints)

Parent: [EPIC] Basic test coverage for all services (aura#175)

To ensure friction-less integration and compatibility with other services, we need a test suite for the Steering API.

These tests should be running as a CI/CD pipeline step and provide these benefits:

• No broken code is committed to main
• The Dashboard test suite is not the only place to uncover bugs or breaking changes (transfer of responsibilities)
• Any API changes are documented and transparent by changes of the test cases
• API consumers, like people at the radio stations using the API, have the added benefit to get a "code example" on how to use the API. This previously was an error prone process, as the API Docs at https://api.aura.radio/steering/ are not fully documented.

Sub Tasks

High priority

Already done by @eigenwijsje:

• /api/v1/users/** (99%)
• /api/v1/rrules/** (read-only)
• /api/v1/notes/** (100%)
• /api/v1/shows/** (100%)
• /api/v1/hosts/** (87%)
• /api/v1/images/** (97%)
• /api/v1/timeslots/** (98%)
• /api/v1/schedules/** (100%) (Collision detection might be good to have 100% plus further thinking about test case which have existing data in the test case, to trigger "special scenarios")

Follow up task

• [EPIC] Steering API integration test suite (med... (#208 - closed)