Is your feature request related to a problem? Please describe.
While auditing the Security Serverless project, we discovered several tables that had multiple sortable columns. These columns look identical to non-sortable ones, which could slow users down or cause confusion. I'd like to consider adding a visual indicator (bold text, semi-transparent icon, etc.) to distinguish sortable columns. Screen shot attached

Describe the solution you'd like
I would like to see a visual indicator and hear an aural indicator that lets me know which columns I can sort on an EuiTable.