Data Table header Affix

[Air-Cooled]

This function solves the problem (这个功能解决的问题)

When have too many rows and do not use paging, I don't want the header to be invisible because of scrolling
Of course the bottom Pagination bar sometimes needs to be Affix

Expected API (期望的 API)

Like：https://demo15.zentao.net/project-bug-15-0-status,id_desc-0-all-0-12-20-1.html

[equt]

track in #1555