Add option to always show the header select-all checkbox without hover

`rowMarkers='checkbox-visible'`

This does make the checkboxes visible for individual rows but users get confused at the select all checkbox which is only visible on hovered. Can we extend this functionality to make select all checkbox to be always visible as well?

https://github.com/user-attachments/assets/b1ce6451-1abe-40e3-bd2c-78cf4c9f4cb9