Proxy SSL Context

What is the feature and why do you need it:

Ability to provide proxy SSL context when creating Configurtion object.

This would be useful in order to configure the TLS connection made to a proxy server, separate from the TLS connection made to the Kubernetes cluster.

This behavior, provided by urllib3, is described here: https://urllib3.readthedocs.io/en/stable/advanced-usage.html#http-and-https-proxies

Please see: HTTPS Proxy + HTTPS Destination

Describe the solution you'd like to see:

Ability to provide proxy SSL context when creating Configurtion object.

https://github.com/kubernetes-client/python/blob/master/kubernetes/client/rest.py#L99

Thanks in advance!