Feature/api user 0.5.2

[bastihav]

Description

Implements user service API v0.5.2
Implements #329

Reason for this PR

• The reasons for the API change were, that we had to fetch every lecturer individually, which was a big performance overhead.

Changes in this PR

• Add new API methods and already implement them in the course list

Type of change (remove all that don't apply)

• Refactoring
• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Ran the unit tests against backend development
• Manually tested all use cases this could alter

Test Configuration:

• OS: Windows

• Browser: Chrome

• Frontend: (remove all that don't apply)

  • Development build

• Backend: (remove all that don't apply)

  • Deployed develop version

Checklist: (remove all that don't apply)

• I have performed a self-review of my own code
• My changes generate no new linting warnings or console warnings
• I have updated the CHANGELOG.md to include any changes made in this PR (add WIP to the top, if there is none already)