Show custom variables visually separated in the host and service detail views

resolves #8966

modules/monitoring/application/views/scripts/show/components/customvars.phtml

@@ -1,3 +1,8 @@
+<tr class="newsection">
+    <td colspan="2">
+        <h4 class="customvar"><?= $this->translate('Custom variables') ?></h4>
+    </td>
+</tr>
 <?php
 
 foreach ($object->customvars as $name => $value) {

modules/monitoring/public/css/module.less

@@ -173,7 +173,8 @@ form.instance-features span.description, form.object-features span.description {
   }
 }
 
-table.avp form.object-features div.header h4 {
+table.avp form.object-features div.header h4,
+table.avp h4.customvar {
   margin: 0;
 }