This adds a WIP implementation of a lightweight Kubernetes client,
or in other words, a kubeconfig parser with some integration with
reqwest to configure auth. It only needs serde_yaml and reqwest.

Ideally this should end up being much smaller than a 'proper' client
and can easily support the few functions we actually care about
(auth, proxies, streamed responses, websockets, exotic kubeconfig
formats, ...).

This at least properly parses all the kubeconfigs I have handy,
including minikube, microk8s, eks, kubeadm, and a few others.

 - bumps reqwest version for proxy support
 - mostly implements KubernetesClient::new()
 - adds notes about all the tls libs being broken :/

Signed-off-by: Tim Buckley <[email protected]>

 - separate enum structs
 - fully implement exec auth
 - honor insecure-skip-tls-verify
 - implement reauthentication and expiry checks for exec auth
   - split `KubernetesClient::new()` and `KubernetesClient::from_context()`