Course Admission API

[bastihav]

Description

• Implements API for course admissions

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

• 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

Test Configuration:

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

Checklist: (remove all that don't apply)

• I added corresponding unit tests (if API code)
• I have performed a self-review of my own code
• I have updated the CHANGELOG.md to include any changes made in this PR (add WIP to the top, if there is none already)