prow: add tests to enforce folder-per-namespace convention for resources #2388
Description
Followup to #2371
Ideally this could be done with conftest
Ensure that for every resource in `infra/gcp/clusters/projects/{project}/{cluster}/resources':
resources/foo.yamlis cluster-scoped (no namespace)resources/{namespace}/foo.yamlhasnamespace: {namespace}
If it turns out the existing resources don't fit this convention, refactor to make them fit
/area prow
/sig testing
/wg k8s-infra
/priority important-longterm