* 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>