Is your feature request related to a problem? Please describe.
We recently implemented draggable fields in Discover, so users can drag and drop fields on the EuiDataGrid and now since you can add fields this way, the next logical step would be to reorder these fields that turned into columns directly using the grid's table headers, without having to use a popover UI. What's more, Discover's EuiDataGrid will be soon become UnifiedDataTable, and replace the grid in Security Solutions Timeline. The current grid supports drag and drop columns ordering with the table headers.

Describe the solution you'd like
The solution how it could look like was drafted in a Figma