* refactor(certificates): replace direct model imports with data classes and APIs
* fix: use Certificates API to create certificates
* docs: update docstring for get_certificate_for_user
* fix: remove trailing whitespace
---------
Co-authored-by: coder1918 <ram.chandra@wgu.edu>
Co-authored-by: Deborah Kaplan <deborahgu@users.noreply.github.com>