Feature Request: delete_supercache capability

### Impacted plugin

Super Cache

### What

Replace edit_other_posts with a custom capability “delete_supercache” or add a filteror add a nice apply_filter(

### How

In wpsc_admin_bar_render() there is a check on a hardcoded capability ( edit_other_posts )
which by default corresponds to the editor and administrator user levels.
This could be replaced with a custom capability “delete_supercache” or add a nice apply_filter() so this capability could be customized to permit/deny the deletion of the entire cache.

Start in wpsc_admin_bar_render() and inspect the hardcoded edit_other_posts capability check. Compare the requested delete_supercache capability with the alternative filter mentioned in the issue, and consider the work done when permissions for deleting the entire cache can be customized.

Written by the indexing model from the issue text.