[v11.0.x] Alerting: Fix max_alerts field handling (#86673)

Alerting: Fix max_alerts field handling (#86651)

Fix max_alerts field parsing

(cherry picked from commit 1b930c341d)

Co-authored-by: Konrad Lalik <konrad.lalik@grafana.com>

public/app/features/alerting/unified/utils/cloud-alertmanager-notifier-types.ts

@@ -320,7 +320,11 @@ export const cloudNotifierTypes: Array<NotifierDTO<CloudNotifierType>> = [
         'max_alerts',
         'Max alerts',
         'The maximum number of alerts to include in a single webhook message. Alerts above this threshold are truncated. When leaving this at its default value of 0, all alerts are included.',
-        { placeholder: '0', validationRule: '(^\\d+$|^$)' }
+        {
+          placeholder: '0',
+          validationRule: '(^\\d+$|^$)',
+          setValueAs: (value) => (typeof value === 'string' ? parseInt(value, 10) : 0),
+        }
       ),
       httpConfigOption,
     ],