prow config: where possible, all config should behave like branchprotector for overrides

[matthyx]

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initial issue: https://github.com/kubernetes/test-infra/issues/9757

The branchprotector override mechanism is amazing and we should use it in every config where people can configure orgs or repos, etc, to allow for more specific overrides. More specifically, plugins like approve have a flat list of configs and don't have any override logic, but users expect it and commit configuration that does nothing.