Migrate image-pushing jobs to use workload identity

[fejta]

/assign @michelle192837 @justaugustus @Katharine

ref #15806

Following

test-infra/config/jobs/kubernetes/test-infra/test-infra-trusted.yaml

Lines 740 to 742 in 3ec967c

	serviceAccountName: deployer # TODO(fejta): should be pusher
	containers:
	- image: gcr.io/k8s-testimages/image-builder:v20200213-0032cdb

[justaugustus]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fejta, justaugustus

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• config/jobs/image-pushing/OWNERS [fejta]

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[k8s-ci-robot]

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

• key k8s-staging-apiserver-network-proxy.yaml using file config/jobs/image-pushing/k8s-staging-apiserver-network-proxy.yaml
• key k8s-staging-apisnoop.yaml using file config/jobs/image-pushing/k8s-staging-apisnoop.yaml
• key k8s-staging-artifact-promoter.yaml using file config/jobs/image-pushing/k8s-staging-artifact-promoter.yaml
• key k8s-staging-capi-openstack.yaml using file config/jobs/image-pushing/k8s-staging-capi-openstack.yaml
• key k8s-staging-cluster-api.yaml using file config/jobs/image-pushing/k8s-staging-cluster-api.yaml
• key k8s-staging-descheduler.yaml using file config/jobs/image-pushing/k8s-staging-descheduler.yaml
• key k8s-staging-e2e-test-images.yaml using file config/jobs/image-pushing/k8s-staging-e2e-test-images.yaml
• key k8s-staging-external-dns.yaml using file config/jobs/image-pushing/k8s-staging-external-dns.yaml
• key k8s-staging-kops.yaml using file config/jobs/image-pushing/k8s-staging-kops.yaml
• key k8s-staging-provider-azure.yaml using file config/jobs/image-pushing/k8s-staging-provider-azure.yaml
• key k8s-staging-release-test.yaml using file config/jobs/image-pushing/k8s-staging-release-test.yaml
• key k8s-staging-service-apis.yaml using file config/jobs/image-pushing/k8s-staging-service-apis.yaml

In response to this:

/assign @michelle192837 @justaugustus @Katharine

ref #15806

Following

test-infra/config/jobs/kubernetes/test-infra/test-infra-trusted.yaml

Lines 740 to 742 in 3ec967c

	serviceAccountName: deployer # TODO(fejta): should be pusher
	containers:
	- image: gcr.io/k8s-testimages/image-builder:v20200213-0032cdb

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