Expose more Kubernetes configuration options

[camertron]

Right now, these are the hoops you have to jump through if, for example, you want to change the deployment's readiness probe:

Kuby.definition('myapp') do
  environment(:production) do
    kubernetes do
      add_plugin(:rails_app) do
        deployment.spec.template.spec.container(:web).readiness_probe do
          timeout_seconds 1  # custom value goes here
        end
      end
    end
  end
end

Obviously that's neither obvious or discoverable, unless you're really familiar with Kuby's source code. Some config options like tls_enabled are already conveniently exposed as properties. It would be nice to expose a bunch of others as properties too. That way, modifying the readiness probe could be as easy as

add_plugin(:rails_app) do
  readiness_timeout 2
end

or even

add_plugin(:rails_app) do
  web_readiness_probe do
    timeout_seconds 2
  end
end

where the call to web_readiness_probe is just a convenience method that returns the web pod's readiness object (which is an instance of KubeDSL::DSL::V1::Probe).