ENH: add "schema" kwarg to io.sql.get_schema method
- [x] closes  #28486
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Picking up #33278
lgtm. @jorisvandenbossche if you can give a once over cc @jorisvandenbossche  lgtm ping on green Green Thanks @arw2019 