Simplify matrix; Use all versions 1.16+ for all distros (#244)

* Simplify matrix; Use all versions 1.16+ for all distros

* Remove non-existent webhook test

* Remove `microk8s.enable helm3` appears redundant and fails

* Link Kubernetes and crictl for K3s|MicroK8s

* Per: #206 (comment)

* Typo

* fix matrix and crictl path

* Consistency and double-quote to expand `${PWD}`

* Temporarily (!) block K3s 1.16 due to hard-coded device plugs (k3s-io/k3s#1390)

* Test mapping K3s 1.16 device plugins to default K8s location

* Create kubectl path in expected location if not present

* Consistent w/ MicroK8s step

* Wait until cluster has stabilized before wrangling device-plugins

* Initial documentation for `run-test-cases.yml`

* Correct indentation

Co-authored-by: bfjelds <bfjelds@microsoft.com>