EPIC - Refactor kn workflow CLI to use client-go instead of `kubectl` subshell calls

Currently, our kn-workflow plugin relies on calls to kubectl subshell in order to interact with the cluster. Ideally, instead, we should use https://github.com/kubernetes/client-go. It's a native golang library and well-documented to connect and manage objects directly within the cluster.

This will easy future feature implementations such as validating if the Operator is installed or Knative is available.

Part of this epic:

[ ] Generate a new client for the SonataFlow Operator API (see https://github.com/apache/incubator-kie-kogito-serverless-operator/pull/185 - already implemented there, we might need to pull this from this PR)
[ ] Refactor the kn-workflow codebase to stop using kubectl subshell (we might need to break this down into smaller tasks after evaluation)

apache / incubator-kie-issues

EPIC - Refactor kn workflow CLI to use client-go instead of `kubectl` subshell calls #1329