[Oblt Onboarding][K8S OTel] Use helm upgrade --install (#215160)

Closes #215134

Using `helm upgrade --install` lets the user run the helm command
multiple times to, for example, upgrade to the new version after a stack
release.

![CleanShot 2025-03-19 at 13 48
39@2x](https://github.com/user-attachments/assets/196c8d6d-1046-44d3-8d44-c300fa0418af)

## How to test

1. Run Kibana and navigate to the K8S OTel onboarding flow
2. Execute snippets provided by the flow
3. Copy only the `helm upgrade --install ...` part of the second snippet
and execute it again
4. Make sure the command succeeds

Co-authored-by: Joe Reuter <[email protected]>

Author: mykolaharmash

x-pack/solutions/observability/plugins/observability_onboarding/public/application/quickstart_flows/otel_kubernetes/otel_kubernetes_panel.tsx

@@ -84,7 +84,7 @@ kubectl create secret generic elastic-secret-otel \\
   --namespace ${namespace} \\
   --from-literal=${elasticEndpointVarName}='${ingestEndpointUrl}' \\
   --from-literal=elastic_api_key='${data.apiKeyEncoded}'
-helm install opentelemetry-kube-stack open-telemetry/opentelemetry-kube-stack \\
+helm upgrade --install opentelemetry-kube-stack open-telemetry/opentelemetry-kube-stack \\
   --namespace ${namespace} \\
   --values '${otelKubeStackValuesFileUrl}' \\
   --version '${OTEL_KUBE_STACK_VERSION}'`