Function upsert_exercise_tasks

async fn upsert_exercise_tasks(
    conn: &mut PgConnection,
    remapped_slides: &HashMap<Uuid, CmsPageExerciseSlide>,
    existing_task_specs: &[ExerciseTaskIdAndSpec],
    task_updates: &[CmsPageExerciseTask],
    retain_exercise_ids: bool,
    spec_fetcher: impl SpecFetcher,
    fetch_service_info: impl Fn(Url) -> BoxFuture<'static, ModelResult<ExerciseServiceInfoApi>>,
) -> ModelResult<Vec<CmsPageExerciseTask>>

Remaps ids from updates to exercise tasks that may have their ids changed.