replay: document is_archived search prop (#13790)

depends on getsentry/sentry#92041

Author: aliu39

docs/concepts/search/searchable-properties/session-replay.mdx

@@ -190,6 +190,12 @@ The event or replay id. In **Issues**, use only the ID value without the `id` ke
 
 - **Type:** UUID
 
+### `is_archived`
+
+Whether the replay has been archived.
+
+- **Type:** boolean
+
 ### `level`
 
 Severity of the event (such as: fatal, error, warning). Always set to info for transactions.