- existing api is not changed
   - load_kube_config works as before
- extend kubeconfig_t to hold in memory buffer
- make a common flow for file/buffer code
- set fileName/buffer members accordingly
- provide new api: load_kube_config_buffer

close filehandle only if we opened one

…uffer is set

Add documentation note stating that only of the kubeconfig_t::fileName and kubeconfig_t::buffer may be set