Remove self-signed TLS cert integration test and replace with unit test

[56quarters]

I haven't been able to get CI to pass on the first try with this project yet. It's nearly always an issue with the integration test for ensuring automatically renewing the self-signed TLS cert works. In order to improve the reliability and our confidence in rollout-operator tests, the test and code under test should be reworked so it can be tested without spinning up an entire Kubernetes cluster.