Multiple Integration Test Slices have become fragile

[tilovillwock]

We need to make a decision on how to allocate resources regarding the following issues:

• a static integration test with a da|ra API call is failing since at least last week (DaraOaiPmhClientTest, see here)
• Embedded MongoDB Framework for integration test fails on newer versions (most likely a JDK version incompatibility)
  • we should at least investigate what version we can update to before tests start to break
• Embedded Elasticsearch Framework for integration tests has been abandoned since 2020 and will fail with the current Elasticsearch LTS release
  • the current version in use (2.11.3) is not even officially released and is being downloaded from the Github Package Registry instead of the usual Maven Package Registry
  • a lot of tests depend on this framework (~47)