Review CI for pinning utilities to specific versions

[phenixblue]

What would you like to be added:

During work on #77 I encountered an issue with a change to the version of the kubectl utility used in the ubuntu-latest GitHub Actions image. v1.19.0 seemed to produce errors for the compare-manifest CI job. I added a ci-bootstrap Make target to download a specific version of kubectl and replace the default in the container image.

Why is this needed:

We should review the work I did and assess the process for more longterm usage and to extend to any other utilities we want (ops, kustomize, kind, etc.). The Gatekeeper project had some examples of doing this that can be used for reference.