text: Title: [Doc] Update user guide for namespace label
  Body: ### What you would like to be added?
  
  Update user guide for the namespace label for metrics collector injection.
  
  ### Why is this needed?
  
  As we discussed in https://github.com/kubeflow/katib/pull/2493#discussion_r1923814931, @andreyvelich suggested that the namespace label for metrics collector injection should not be patched in the Python SDK. We need to update the user guide to inform users of the effect of this label.
  
  /cc @kubeflow/wg-automl-leads @helenxie-bit @tariq-hasan @Doris-xm @truc0 
  
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