Allow configuring log output from traffic router plugins

[FredrikAugust]

Summary

As of now, it seems like log output from the core application and traffic router plugins are handled differently, which makes it a little hard to work with. I've seen the issue #4042 which I suppose would resolve this.

time="2025-02-06T10:18:15Z" level=info msg="Reconciliation completed" generation=195 namespace=xyz resourceVersion=588835099 rollout=xyz time_m[snip]
2025-02-06T10:18:15.328Z [DEBUG] plugin.gatewayAPI: time="2025-02-06T10:18:15Z" level=info msg="[SetWeight] plugin \"argoproj-labs/gatewayAPI\" con[snip]

It would be nice if the output from the child plugin would instead be put inside the msg field of a normal log message.

Use Cases

When using a traffic router plugin this would make it easier to add good observability.

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