Change k8s API removals from error to warning

[lblackstone]

Proposed changes

The provider checks for deprecated and removed API
versions of k8s resources to provide clearer messages
for affected APIs. These messages are intended to be
informational, and should not block the deployment of
a resource if the cluster accepts it. To avoid inadvertently
failing a deployment when the upstream removal version
has changed, print a warning rather than returning an error.

Here's what this looks like now for a removed API:

Preview

warning: apiVersion "extensions/v1beta1/Deployment" was removed in Kubernetes 1.16. Use "apps/v1/Deployment" instead.
See https://git.k8s.io/kubernetes/CHANGELOG/CHANGELOG-1.16.md#deprecations-and-removals for more information.

(This previously would have returned an error)

Update

error: resource scale-test was not successfully created by the Kubernetes API server : apiVersion "extensions/v1beta1/Deployment" was removed in Kubernetes 1.16. Use "apps/v1/Deployment" instead.
See https://git.k8s.io/kubernetes/CHANGELOG/CHANGELOG-1.16.md#deprecations-and-removals for more information.

(An error is returned, but it's only after the cluster reported that the resource was not available.)

Related issues (optional)

Related to #1388