Expand automated testing to cover more k8s distributions and versions

**Describe the problem/challenge you have**
Sometimes people run kapp-controller on something other than minikube. Weird, right? I thought this whole kubernetes thing was for turning developer laptops into space heaters during the winter months, and then in the summer we shed our winter coats and run applications on bare metal again? But anyways, whoever these people are running our tool in "the cloud", it turns out sometimes we have compatibility issues. In order to support all clouds of digital troposphere, from the noble cirrus to the humble cumulonimbus, we should test against them!

**Describe the solution you'd like**
We should probably test against at least AWS and GC?
There's something vaguely close to prior art in impgkg: https://github.com/vmware-tanzu/carvel-imgpkg/blob/develop/.github/workflows/gh-test-external-registry.yml#L59

**Anything else you would like to add:**
Definitely related to the discussion in https://github.com/vmware-tanzu/carvel-kapp-controller/issues/352 in spirit, - at some point there's a matrix of kubernetes versions x kubernetes providers.

Likely a good first step on this issue would be to peel off a single deliverable, like "we'll test kubernetes 1.22 on Google Cloud"; this is intended more as an "epic" or "parent issue".

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