enable hpa-values.yaml test in helm charts e2e test in CI

[daisy-ycguo]

No description provided.

[eero-t]

@daisy-ycguo CI needs Prometheus for testing hpa-values.yaml: https://github.com/opea-project/GenAIInfra/blob/main/helm-charts/HPA.md#prometheus

Otherwise Helm install fails due to missing serviceMonitor and custom metrics Kubernetes APIs.

As to testing that the HPA rules actually work, there's a manual step needed for installing the required custom metric config. That part can be scripted in few lines, shown here: https://github.com/opea-project/GenAIInfra/blob/main/helm-charts/HPA.md#post-install

TGI and TEI services enabled their metrics enpoints only after processing their first request. I.e. verifying that that HPA can access the relevant custom metrics, requires uploading doc(s) with data-prep so that reranking is used, and doing at least one ChatQnA query. Then HPA can be verified to be working:
https://github.com/opea-project/GenAIInfra/blob/main/helm-charts/HPA.md#verify