EscalationCondition.php: Set default operator value

For the `incident_age` column, the `operator` select is disabled and
only offers a single option (`>`). Disabled HTML selects don't submit
a value, so the operator was previously missing from the submitted
data and form could not be submitted. Defaulting the element's value
to the first available option ensures it's always set, even while
disabled.

Author: sukhwinder33445

application/forms/EventRuleConfigElements/EscalationCondition.php

@@ -135,6 +135,7 @@ protected function assemble(): void
         $this->addElement('select', 'operator', [
             'required' => true,
             'options' => $operators,
+            'value' => array_key_first($operators),
             'disabled' => $selectedColumn === 'incident_age'
         ]);