Update user guide for namespace label in Katib Python SDK example (#3976)

* doc(katib): add guidance of namespace label configuration in Getting-Started

Signed-off-by: Xinmin Du <[email protected]>

* doc(katib): move guidance to Metrics Collector, add note in getting-start

Signed-off-by: Xinmin Du <[email protected]>

* Update content/en/docs/components/katib/user-guides/metrics-collector.md

Co-authored-by: Shao Wang <[email protected]>
Signed-off-by: Du Xinmin <[email protected]>

---------

Signed-off-by: Xinmin Du <[email protected]>
Signed-off-by: Du Xinmin <[email protected]>
Co-authored-by: Shao Wang <[email protected]>

Author: Doris-xm

Diff for: content/en/docs/components/katib/getting-started.md

@@ -39,6 +39,11 @@ If you install Katib as part of Kubeflow Platform, you can open a new
 **Note**. If you use Katib within Kubeflow Platform to run this example, you need to use this
 namespace: `KatibClient(namespace="kubeflow-user-example-com")`.
 
+**Note**. The `kubeflow` namespace is pre-configured with the required label 
+`katib.kubeflow.org/metrics-collector-injection: enabled` for metrics collection. If you want to use pull-based metrics collector 
+in other namespaces, you can attach this label following the instructions in the 
+[Metrics Collector](/docs/components/katib/user-guides/metrics-collector/#prerequisites).
+
 ```python
 # [1] Create an objective function.
 def objective(parameters):

Diff for: content/en/docs/components/katib/user-guides/metrics-collector.md

@@ -6,6 +6,30 @@ weight = 40
 
 This guide describes how Katib metrics collector works.
 
+## Prerequisites
+
+Before running your hyperparameter tuning Katib Experiment with Python SDK,
+ensure the namespace label `katib.kubeflow.org/metrics-collector-injection: enabled`
+is present. This label enables the sidecar container injection for pull-based metrics collectors to collect metrics during the experiment.
+
+You can configure the namespace by adding the following label `katib.kubeflow.org/metrics-collector-injection: enabled` 
+as is shown in the sample code:
+
+```yaml
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: <your-namespace>
+  labels:
+    katib.kubeflow.org/metrics-collector-injection: enabled
+```
+
+Or you can add the label to an existing namespace using the following command:
+
+```bash
+kubectl label namespace <your-namespace> katib.kubeflow.org/metrics-collector-injection=enabled
+```
+
 ## Overview
 
 There are two ways to collect metrics: