[Table] Emit event on function "onChange" when user select/unselect all rows by clicking on header checkbox

[Esteban Sorribas]

Description

I think this would be interesting to who uses the table component with pagination from backend API and needs to know if user has selected the whole dataset.

For example: selecting all rows for export to excel.

Additional context

Example:

function onChange (checked: boolean) {
      if (checked) {
        selectAllRows()
      } else {
        selected.value = []
      }
      
      // Add emit here
      emit('select:all', checked)
    }