issue #27642 - timedelta merge asof with tolerance
- [X] closes #27642 
- [x] tests 2 / 1 [added / passed] 
- [X] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
- [ ] \(Optional) allow users to pass datetime.timedelta objects for tolerance