Allow to use Telepresence mounted volumes with in_cluster_config

[nevalla]

Telepresence mounts service account's token and ca cert in $TELEPRESENCE_ROOT/var/run/secrets/kubernetes.io/serviceaccount/ path. Would be nice if we could allow to use this files with in_cluster_config method.

[kke]

It's possible to pass the ssl_ca_path and auth token manually, but it could still try to use the TELEPRESENCE_ROOT when set.

[kke]

Looks like not via K8s::Client.in_cluster_config which does not pass the **options.