Install the agent with Helm chart instead of k8s manifests in our QA test

The following discussion from !104889 (merged) should be addressed:

• @Alexand started a discussion: (+1 comment)

  Newer agentk versions also required these environment variables to be deployed.

  Ideally, we should actually install agentk with Helm, but our Helm chart does not yet support configuring headers.

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Our chart already supports adding headers to agentk requests. Maintaining a manifest installation inside of the qa framework of the agent does not make sense. It's way easier and much better to just maintain the chart and use it to install the agent in the qa framework.