include label with percentage values (via expressions)

Author: kamilkisiela

packages/web/docs/src/content/router/configuration/override_labels.mdx

@@ -100,9 +100,14 @@ Within the `expression`, you have access to the following context:
 
 ```yaml
 override_labels:
-  activate_beta_feature:
+  # This label will be active for 5% of the traffic
+  use-fulfillment-service:
+    expession: 'random_float(0.0, 100.0) < 5.0'
+
+  activate-beta-feature:
     expression: '.request.headers."x-user-group" == "beta"'
 ```
 
-This configuration activates the `activate_beta_feature` label only for requests that include the
-header `x-user-group: beta`.
+This configuration activates the `activate-beta-feature` label only for requests that include the
+header `x-user-group: beta`. The `use-fulfillment-service` label is activated for approximately 5%
+of all requests, enabling a canary release pattern.