Need a flag to explicitly add a root certificate for the access to a remote cluster behind a corp proxy

[tuwchia]

Problem encountered

I have run kube-explorer with the following command:

kube-explorer --kubeconfig=C:\Users\john\Documents\k3s.yaml --http-listen-port=9898

However, the output is full of the : x509: certificate signed by unknown authority error.

Suggestion

Since the access to the remote cluster is over https, the certificate provided by the proxy server must be added as the root certificate before the curl command can work properly.

So add a flag for users behind corp proxies to specify the certificates of their proxy servers.

[niusmallnan]

refer to #18