Add difficulty to the quiz

[KhaninPasha0488]

Frontend:

• [ ] Add sorting by difficulty
• [ ] Make filtering by difficulty

Backend:

• [ ] Add the "difficulty" field to the quiz
• [ ] The difficulty of the quiz should be determined based on the results of the difficulty of all questions.

Example: difficultyQuestionType : 'light' | 'medium' | 'hard'} const difficultyQuestion =()={ If('light') {return 1} If('medium') {return 2} If('hard') {return 3} } const difficultyQuiz = sum of difficultyQuestion / number of difficultyQuestion If(difficultyQuiz < 1.5) {return 'light'} If(difficultyQuiz >= 1.5 & difficultyQuiz < 2.5) {return 'medium'} If(difficultyQuiz <= 2.5) {return 'hard'}