[BugFix] QA pipeline edge case: `align_to_words=True` in `QuestionAnsweringPipeline` can lead to duplicate answers (#38761)
* fixing the problem align_to_words=True leading to duplicate solutions
* adding tests
* some fixes
* some fixes
* changing the handle_duplicate_answers=False by default
* some fixese
* some fixes
* make the duplicate handling the default behaviour and merge duplicates
* make the duplicate handling the default behaviour