migrate away from test-infra-trusted build cluster

[ameukam]

There are a few jobs running on the test-infra-trusted we should either migrate to k8s-infra-prow-build-trusted or remove:

• post-test-infra-push-git
• post-test-infra-push-git-custom-k8s-auth
• post-test-infra-upload-testgrid-config
• ci-test-infra-update-slack-oncall

[ameukam]

/assign @michelle192837
/sig testing

[BenTheElder]

ci-test-infra-update-slack-oncall

no point migrating this, we'll just shut it down when prow is migrated and instead people can posted in #testing-ops in slack.

we should actually probably proactively stop advertising @test-infra-oncall to the broader project.

post-test-infra-upload-testgrid-config

.... uhhhh this one I'm not sure, because we have to be able to publish to testgrid's config bucket .... migrating testgrid is another fun topic

The image publishing jobs we should be able to move over.

[michelle192837]

re: ci-test-infra-update-slack-oncall: Ah, that's easier then.

re: post-test-infra-upload-testgrid-config: I think this should be doable. I have not gone through the full details, but imo thanks to config merger merging configs for TestGrid from multiple locations, we can stand up a new config upload job in community-owned infra, verify the uploaded config in the new location is the same as the old, and swap the config location used in the TestGrid instance overall.