[7.13] [DOCS] Adds missing monitoring.cluster_alerts.email_notifications.enabled setting (elastic#127323) (elastic#127385)

Co-authored-by: Spencer <[email protected]>

Author: KOTungseth

docs/settings/monitoring-settings.asciidoc

@@ -31,6 +31,10 @@ For more information, see
 
 [cols="2*<"]
 |===
+| `monitoring.cluster_alerts.email_notifications.enabled`
+  | deprecated:[7.11.0] 
+  When enabled, sends email notifications for Watcher alerts to the specified email address. The default is `true`. 
+  
 | `monitoring.cluster_alerts.email_notifications.email_address` {ess-icon}::
   | deprecated:[7.11.0] 
   When enabled, specifies the email address where you want to receive cluster alert notifications.