Using th to control table-pin-cols is inconvenient

[bogdan]

Currently table-pin-cols expects certain rows to use <th> instead of </td> to be sticky. This is inconvenient for a number of reasons:

1. th has a default styling from browser that you might not want
2. Documentation says that "The tag defines a header cell in an HTML table". So it is not very semantic to use them outside of header.
3. Other header cells can not use th anymore even though they are header cells.
4. Conditional tag generation between td and th based on stickiness leads to complexity in code. I can imagine it can be even harder in react.

Example of it looks like in my source code:

= content_tag(column.options[:sticky] ? :th : :td, class: ['align-text-top', datagrid_column_classes(grid, column)] ) do
  .text-xl.mb-1= column.header

I think it would be so much better to control stickiness with a class like table-cell-sticky than a tag.