feat(alerts): Add info about custom metric alerts limitation (#12797)

Author: priscilawebdev

docs/product/alerts/create-alerts/metric-alert-config.mdx

@@ -101,7 +101,7 @@ This feature is only available to organizations with a Business or Enterprise pl
 
 </Alert>
 
-A wider variety of fields or tags are available in addition to the basic properties mentioned above, so you can create more advanced filtering conditions. However, Sentry only starts collecting these metrics after the alert is saved. If such a filter is used, Sentry provides an estimate of the metric for the previous period during the alert's creation.
+A wider variety of fields or tags are available in addition to the basic properties mentioned above, so you can create more advanced filtering conditions. However, Sentry only starts collecting these metrics after the alert is saved. If such a filter is used, Sentry provides an estimate of the metric for the previous period during the alert's creation. A maximum of 50 alerts with advanced filters is allowed per project on certain legacy plans.
 
 ![Advanced filters for transactions](./img/alerts-advanced-filters.png)