Simplify configuration

[kke]

Addresses parts of #121

• The Dry-Struct -mapped K8s::Config is replaced with an unvalidated and unstructured hash. Validating kubeconfig -files is not in the scope of k8s-client. In the future, this can lead to dropping the dry-dependencies, making the client easier to use in projects that have dry-dependecies of their own, which seem to generate a lot of dependency issues.
• Instead of RecursiveOpenStruct, the config uses a simple selfmade hash-extension that pretty much works the same. Later the dependency can be dropped and api-responses returned as these dot-notated hashes.
• Tries the /etc/kubernetes/admin.conf and /etc/kubernetes/kubelet.conf when autoconfiguring, making k8s-client work with zero config when running on kube nodes.
• Some of the config code was copied and adapted from Pharos::Kube::Config which handles pretty much the same task with considerably less code than k8s before this pr.

Specs pass but still needs some cleanup and yardoc fixes.

[kke]

Outdated and weird, reimplement some other way.