API/BUG: Fix Series ops inconsistencies
- [x] closes #1134, closes #4581, closes #13538
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry

This includes the fix only for #1134 and not for other inconsistencies (like #13637), as it needs further discussions.

Changes:
- series comparison operator to check whether labels are identical (currently: ignores labels)
- series boolean operator to align with labels (currently: only keeps left index)
