javadoc and testclasses for backend

removed list of answers from QuizResultDTO and added quizResultId til QuestionAnswerDTO to have same correlation as Quiz has to question

requested review from @torbjant

assigned to @heinemb

added 13 commits

• 832a6281...79d0501d - 12 commits from branch main
• 4327b1b0 - Merge branch 'main' into 'addition'

Compare with previous version

merged

mentioned in commit 13976d4b