Add auth checks to EventTransformer

[creydr]

Currently the EventTransformer does not enforce authentication nor authorization. This was mostly, as the data-plane was written in nodejs.
With #8708 we got an auth-proxy which can be added as a sidecar and does the auth checks, before passing the request.
We should integrate this auth-proxy similar as we've done it for the IntegrationSink.

[github-actions]

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