List features in relay docs (#9371)

Co-authored-by: Iker Barriocanal <[email protected]>
Co-authored-by: vivianyentran <[email protected]>

docs/product/relay/projects.mdx

@@ -108,3 +108,17 @@ An empty list rejects all origins. Use the default `["*"]` to allow all origins.
   }
 }
 ```
+
+`config.features`
+
+Some Sentry product features are disabled by default in Relay, either because they are still experimental or because they are not available on all plans. In static mode, these features have to be enabled manually if needed.
+
+```json
+{
+  "config": {
+    "features": ["organizations:session-replay"]
+  }
+}
+```
+
+A full list of features you can enable can be found [here](https://getsentry.github.io/relay/relay_dynamic_config/enum.Feature.html#variants).