Add explicit step to enable Prometheus stack in generated_values.yaml

Users installing Robusta + Prometheus now have a clear step to add
enablePrometheusStack: true to their generated_values.yaml file.

Author: claude

docs/setup-robusta/installation/all-in-one-installation.rst

@@ -19,6 +19,15 @@ Prerequisites
    :header_update_levels:
    :file: setup-robusta/installation/_generate_config.jinja
 
+Enable Prometheus Stack
+------------------------------
+
+Add the following to your ``generated_values.yaml`` file:
+
+.. code-block:: yaml
+
+    enablePrometheusStack: true
+
 .. include:: ./_helm_install_with_prometheus.inc.rst
 
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