ENH: Support index=True for io.sql.get_schema
Closes pandas-dev/pandas#9084

- Decided to keep the default as `index=False` to keep the API consistent. `to_sql` has `index=True`.
- Tempted to name the parameter `include_dataframe_index` as "index" has
a different meaning in a SQL context.

- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
