Add a flag in tracing config to use service instead of pod name

[pomyslowynick]

Add a flag in tracing config to use service instead of pod name

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 this issue and would still be relevant after the migration to OTel.

From my own experience, service.name is used to group the traces together and when it's set to the pod name it's impossible to keep them all together.

This flag is a noop for existing configurations, since it defaults to false and will be used in another PR
I've tested it in a live cluster for true/false/undefined values in the config map, in all the cases it worked as expected.

/kind enhancement

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.

[knative-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: pomyslowynick
Once this PR has been reviewed and has the lgtm label, please assign cali0707 for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[linux-foundation-easycla]

• ✅login: pomyslowynick / (9d7b785)
• ✅login: pomyslowynick / (9d7b785, 0814539)
• ✅login: pomyslowynick / (9d7b785, 0814539, 563a1a3)

The committers listed above are authorized under a signed CLA.

[knative-prow]

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

[knative-prow]

Hi @pomyslowynick. Thanks for your PR.

I'm waiting for a knative member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[dprotaso]

/hold

I want to revisit this after the next release (Apr 22) - I think for the subsequent release we should do real work to migrate to OTel. Supposedly they are removing OpenCensus support in the OTel collector.