Make InClusterConfigLoader support explicit config parameter

[GlassOfWhiskey]

Configuration related classes KubeConfigLoader and InClusterConfigLoader behave differently in the load_and_set method. The first one requires an external Configuration object, which can be either automatically generated or passed explicitly by the user in the load_kube_config function.
Conversely, the InClusterConfigLoader only supports the automatically generated default Configuration object. This does not support situations in which a Python client must connect to both the local Kubernetes cluster and a remote cluster in the same run.
A simple fix would be to harmonize the behaviour of the two objects by passing an explicit config object to the load_and_set method of the InClusterConfigLoader class and a client_configuration object to the load_incluster_config function. Backward compatibility can be ensured by defaulting those parameters to None and keeping the actual behaviour in case of None inputs.

[GlassOfWhiskey]

I have no problems in providing a PR also for this issue if needed.

[tomplus]

Thanks for reporting this. Your proposed fix looks good to me. It'd be fantastic if you could work on it.