Run system tests in PR pipeline with all versions of Kubernetes server

[coro]

Is your feature request related to a problem? Please describe.
Currently, the system tests run against whatever the default version of Kubernetes is for the version of kind stored in go.mod. Currently, that is 1.18, switching to 1.19 in #339 .

Due to the breaking nature of Kubernetes minor version bumps, it is difficult to know if a PR breaks compatibility with older versions of Kubernetes, and fairly inexpensive to run the system tests against kind clusters of all supported minors in parallel in the PR workflow.

Consider changing the workflow to test across all supported minor versions.