releng: setup service account to be used in prow build to access gcb

[cpanato]

The PR tries to address the feedback kubernetes/test-infra#20703 (comment) to be able to run pre-submits jobs to trigger GCB

To be honest I'm not sure if those changes are correct. Please let me know what we need to update/create.

Follow up

• create a check to add some enforcement around which jobs are allowed to use which service accounts via tests in config/tests/jobs in test-infra repo.

Related to kubernetes/release#1850

/assign @spiffxp @hasheddan

[spiffxp]

/approve
/lgtm
/hold
/assign @dims @spiffxp
Remove hold when ready to deploy

[hasheddan]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cpanato, hasheddan, spiffxp

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[spiffxp]

/hold cancel

[spiffxp]

hm, tide is currently saying "Pending — Not mergeable." but the details link says the PR is good to merge

other info:

• https://prow.k8s.io/tide shows no pool with this PR in it at present
• https://prow.k8s.io/tide-history shows no history indicating action on this PR

maybe posting this comment will refresh things?

[spiffxp]

Upon closer inspection this won't quite work, the project names don't quite line up. I'm going to open a followup PR to make a gcb-builder-releng-test@k8s-staging-releng-test service account, and give it GCB and GCR access.

[spiffxp]

Opened #1626