docs: Update watcher cr spec manager field

docs/api.md

@@ -38,6 +38,18 @@ spec:
 
 It uses either the `spec` or `status` value to define if Runtime Watcher sends an event to KCP if the spec of the specified GVK or the status changes.
 
+### **spec.manager**
+
+Specifies the component responsible for handling webhook requests from Runtime Watcher. This field determines the routing path for webhook validation requests to KCP (`/validate/<manager-value>`).
+
+```yaml
+spec:
+  manager: "lifecycle-manager"
+```
+
+> ### Note:
+> **Backward Compatibility:** If you don't set **spec.manager**, the system falls back to the `operator.kyma-project.io/managed-by` label for backward compatibility. However, this label-based approach is deprecated and will be removed in a future version. It is recommended to migrate to using the **spec.manager** field.
+
 ## KCP configuration
 
 ### **spec.serviceInfo**
@@ -65,4 +77,7 @@ spec:
 
 ## Labels
 
-- **`operator.kyma-project.io/managed-by`:** This label specifies the module that manages and listens the Watcher CR's corresponding webhook. The value of this label is used to generate the path in KCP for the Watcher webhook's requests - `/validate/<label-value>`.
+- **`operator.kyma-project.io/managed-by`:** **[DEPRECATED]** This label previously specified the module that manages and listens to the Watcher CR's corresponding webhook. The value was used to generate the path in KCP for webhook requests (`/validate/<label-value>`). 
+
+> ### Caution
+> The `operator.kyma-project.io/managed-by` label is deprecated. Use the **spec.manager** field instead. The label-based fallback will be removed in a future API version. For more information, see the [**spec.manager**](#specmanager) section.