kubectl needs support for dcos EE authentication

[jdef]

• kubectl subcommand needs to fetch token from local dcos.toml file
• kubectl binary needs to send Authorization: header for dcos EE compat

[jdef]

tentative plan is this:

• create a dcos-kubectl binary, copy/paste of k8s/cmd/kubectl, except:
• invokes kubectl/cmd/util.NewFactory with a custom config that:
  • provides SSL information
  • provides a WrapTransport func that injects the DCOS token into the request headers

[jdef]

custom k8sm-kubectl binary: https://github.com/kubernetes/kubernetes/pull/21527

[jdef]

proposed a plugin-based approach for kubectl: https://github.com/kubernetes/kubernetes/pull/21553

• awaiting greenlight

[jdef]

upstream likely going this way: https://github.com/kubernetes/kubernetes/pull/23066