Add "No data available" display when list is empty (#33517)

Add a "No data available" message to be displayed when the list has no
data. This improves the user experience by providing clear feedback in
an empty state.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/admin/emails/list.tmpl

@@ -67,6 +67,8 @@
 								>{{svg "octicon-trash"}}</a>
 							</td>
 						</tr>
+					{{else}}
+						<tr><td class="tw-text-center" colspan="6">{{ctx.Locale.Tr "no_results_found"}}</td></tr>
 					{{end}}
 				</tbody>
 			</table>