Made many changes to use uuid instead of the id
- Add functionalities to get chapters by subject uuid.
- Add Exercise attempt functionalities: start and submit exercise attempt.
- Made changes in subject controller: get subject by child id, get specific subject by id and by uuid, get subject categories.
- Made changes in the responses DTOs to use uuid instead of the id.
- Change also the mappers to modify the id by the uuid, and add new mapping for the new DTOs.
- Change also the repositories to use the uuid instead of the id.
- NOTE: There is still some IDs in responses that it will be handeled by another collegue responsable of them.