add trust-manager to periodic-testing Prow jobs

[erikgb]

To keep the community focused on the most important (and popular/fresh) issues and pull requests, I propose including trust-manager in the periodic-testing Prow jobs that run for cert-manager.

[cert-manager-prow[bot]]

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[inteon]

Thanks Erik, code looks like expected. LGTM

[cert-manager-prow[bot]]

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

• key testing-periodics-trusted.yaml using file config/jobs/testing/testing-periodics-trusted.yaml

In response to [this](https://github.com/cert-manager/testing/pull/1069): >To keep the community focused on the most important (and popular/fresh) issues and pull requests, I propose including trust-manager in the periodic-testing Prow jobs that run for cert-manager. Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes-sigs/prow](https://github.com/kubernetes-sigs/prow/issues/new?title=Prow%20issue:) repository.