add r2 release creds to gcp release-builder publish jobs for 1.29 and 1.30

[PetrMc]

publish.sh on release-1.29/1.30 uploads to R2 since istio/release-builder#2419 and istio/release-builder#2420 but the gcp publish jobs never got cf-r2-istio-release-auth, so 1.29.8 and 1.30.5 publish failed with CF_CREDENTIALS unbound. Matches the release-1.31 aws job.

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[PetrMc]

also dropped the istio-ecosystem main/1.31 sail-operator dashboards from testgrid: #6041 moved those jobs to aws but the configurator (both the presubmit check and the trusted upload to gs://istio-testgrid) only reads prow/gcp/cluster/jobs, so they had no tabs and the check has been failing since sep 16. reverted the config_test.go merge from #6041 so the go test matches what prod generates, same as #6008 did for the istio jobs

[fjglira]

Lgtm. Let's rerun and check

[istio-testing]

@PetrMc: Updated the job-config configmap in namespace default at cluster default using the following files:

• key istio.release-builder.release-1.29.gen.yaml using file prow/gcp/cluster/jobs/istio/release-builder/istio.release-builder.release-1.29.gen.yaml
• key istio.release-builder.release-1.30.gen.yaml using file prow/gcp/cluster/jobs/istio/release-builder/istio.release-builder.release-1.30.gen.yaml

Details

In response to this:

publish.sh on release-1.29/1.30 uploads to R2 since istio/release-builder#2419 and istio/release-builder#2420 but the gcp publish jobs never got cf-r2-istio-release-auth, so 1.29.8 and 1.30.5 publish failed with CF_CREDENTIALS unbound. Matches the release-1.31 aws job.

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