* core: replace GetMiddleware
See the discussion in #881. GetMiddleware would add a `nil` middleware
to the callstack thereby breaking functionality.
This PR drops it in favor of RegisterHandler which is a completely
standalone registry for middleware that want to let it self know to
other middleware.
Currenly *autopath* uses this to call *kubernetes*'s AutoPath method
for dynamic autopathing.
* Drop GetMiddleware
* Register metrics
* drop the panic
* middleware/authpath: Fix return from k8s mw
Return the correct search path from the kubernetes' AutoPath function.
Based on preliminary discussion in #870
* PodWithIP can be private
Fix and add docs to functions.
* CR: remove the error from AutoPathFunc
