EHN: to_{html, string} col_space col specific
- [ ] closes #28917
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

In to_html, to_latex and to_string, ```col_space``` arg now accepts a list or dict where we can mention the column name to change only a specific column's width.
Haven't add test for to_latex and to_string since they too don't have test for the old col_space and I cannot think of anything less cumbersome than to count added whitespace.