Add an option to generate a reference configuration from a running cluster

[dcritch]

It would be useful to have the ability to capture resources from a running Kubernetes cluster and generate a reference directory + metadata.yaml compatible with the tool. It would allow for easier comparisons between different running clusters, as well as generating manifests from a cluster in a known, good state. A configuration file can be supplied so that only desired objects are captured in the output artifacts.

[dcritch]

Using my python version as inspiration, I've got something working in a branch here: https://github.com/dcritch/kube-compare/tree/generate-reference

It adds a -g option to generate a reference config. Should I go ahead and make a PR, or should we discuss the implementation a bit more first?