added the custom icon and username for the outgoing webhook and its response (#9141)

* 8272 added the username and icon as part of the model and persisted the same

* 8272 added the custome icon and name when set to the web hook response

* 8272 changed the infinte loop to timeout after 5 seconds

* 8272  fixed review comments

store/sqlstore/webhook_store.go

@@ -61,6 +61,8 @@ func NewSqlWebhookStore(sqlStore SqlStore, metrics einterfaces.MetricsInterface)
 		tableo.ColMap("Description").SetMaxSize(128)
 		tableo.ColMap("ContentType").SetMaxSize(128)
 		tableo.ColMap("TriggerWhen").SetMaxSize(1)
+		tableo.ColMap("Username").SetMaxSize(64)
+		tableo.ColMap("IconURL").SetMaxSize(1024)
 	}
 
 	return s