docs(eks): corrects url of stable helm charts (#22691)

URL of included helm chart collection was changed in 2020 per [Helm Blog](https://helm.sh/blog/new-location-stable-incubator-charts/)

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Author: misterjacko

packages/@aws-cdk/aws-eks/lib/helm-chart.ts

@@ -30,7 +30,7 @@ export interface HelmChartOptions {
   readonly version?: string;
 
   /**
-   * The repository which contains the chart. For example: https://kubernetes-charts.storage.googleapis.com/
+   * The repository which contains the chart. For example: https://charts.helm.sh/stable/
    * @default - No repository will be used, which means that the chart needs to be an absolute URL.
    */
   readonly repository?: string;