Add a config flag to use service name in traces

[pomyslowynick]

Proposed Changes

• Use a flag to use ServingServiceas the trace service.name which is added in this PR

Motivation is pretty much the same as in the other PR, copy pasting:

While the OTel migration is in progress it would be very helpful to have a flag which allows users toggling the ServingService to be used as the service.name in traces.
This is related to #12969 and would still be relevant after the migration to OTel.

Release Note

You can now use the `useServingService` flag in the tracing config to use the `ServingService` as the `service.name` in traces. Current default is to use the `ServingPod` as the `service.name`, and it remains the same if the flag is not set.

[linux-foundation-easycla]

• ✅login: pomyslowynick / (3c021e5)

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[knative-prow]

Welcome @pomyslowynick! It looks like this is your first PR to knative/serving 🎉

[knative-prow]

Hi @pomyslowynick. Thanks for your PR.

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[knative-prow]

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[dprotaso]

/hold

Made a comment here - knative/pkg#3164 (comment)

I want to revisit our OTel approach after the next release. That might require breaking changes and we'd probably make this change without a config map flag.

[pomyslowynick]

/hold

Made a comment here - knative/pkg#3164 (comment)

I want to revisit our OTel approach after the next release. That might require breaking changes and we'd probably make this change without a config map flag.

Happy to help with OTel migration if that brings us closer to resolving this issue, if there's a need.