Updates Alerts to include custom metrics (#10179)

* Updated Alert Creation screenshot

Update Alert Creation screenshot to include custom metrics

* Updated Metric Alerts

Updated Metric Alerts configuration to include custom metrics

Author: ale-cota

docs/product/alerts/create-alerts/img/create-new-alert-rule.png

@@ -35,6 +35,10 @@ When creating new metric alerts, the `is:unresolved` filter is added by default.
 - Largest Contentful Paint
 - First Input Delay
 - Cumulative Layout Shift
+- Custom Measurement
+
+#### Metrics
+- Custom Metric
 
 ### Functions for Metric Types
 
@@ -85,10 +89,11 @@ For some metric alerts, you can set the event type that you want to be alerted a
 
 ### Tags & Properties
 
-Add filters in the provided input to narrow down what you'll be alerted about, such as transaction tags or other event properties. Available properties depend on your alert's event type:
+Add filters in the provided input to narrow down what you'll be alerted about, such as tags or other event properties. Available properties depend on your alert's type:
 
 - For **error** events, all error properties are available. See [Searchable Properties](/product/sentry-basics/search/searchable-properties/events/#searchable-properties) for a full list.
 - For **transaction** events, the following basic properties are generally available: `release`, `transaction`, `transaction.status`, `transaction.op`, `http.method`, `http.status_code`, `os.name`, `browser.name`, and `geo.country_code`.
+- For **metrics**, all (metric tags)[/product/metrics/#augmenting-metrics-with-tags] are available.
 
 #### Advanced filters for Transactions