ENH: Add ignore_index for df.sort_values and series.sort_values
- [x] xref #30114 
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

This is the first step for closing the PR #30114, I will come up with another PR for `drop_duplicates`
thanks @charlesdong1991 