(APG-314d) Add client and service methods to call course-participations/referral/{id}

[jsrobertson]

Context

We need to get the course participations added by referral id so we can show them when creating a draft referral.

Changes in this PR

Add Course client and service methods to call /course-participations/referral/{id}

Release checklist

Release process documentation

As part of our continuous deployment strategy we must ensure that this work is
ready to be released once merged.

Pre-merge

• There are changes required to the Accredited Programmes API for this change to work...
  • ... and they have been released to production already

Post-merge

• This adds, extends or meaningfully modifies a feature...
  • ... and I have written or updated an end-to-end test for the happy path in the Accredited Programmes E2E repo
• This makes new expectations of the API...
  • ... and I have notified the API developer(s) of changes to the contract tests (Pact), or the API is already compliant
• Manually approve release to preprod
• Manually approve release to prod