Update editMonitorBodyValidation to disallow empty notifications

Server/validation/joi.js

@@ -229,7 +229,7 @@ const editMonitorBodyValidation = joi.object({
 	name: joi.string(),
 	description: joi.string(),
 	interval: joi.number(),
-	notifications: joi.array().items(joi.object()),
+	notifications: joi.array().items(joi.object()).min(1),
 });
 
 const pauseMonitorParamValidation = joi.object({