Add possibility to get ILoadBalancer by name and instance of IClientConfig

[Savonitar]

Hi everybody!
I'd like to get ILoadBalancer by providing the name and IClientConfig instance. Currently we only have a way with Class<? extends IClientConfig> and in this case we will create an instance via newInstance() method.
But I need to provide the clientconfig instance created by myself, because it could be created with some additional parameters, could be configured in a special way (especially when i have to provide some parameters dynamically). In other words I need to provide the prepared IClientConfig instance instead of creation a new one.
Also I want to return an existed loadbalancer (if it exists), that's why I can't use registerNamedLoadBalancerFromclientConfig method because it throws an exception if the balancer exists.
Currently I use reflection to get an access to namedLBMap to get balancer by name and call registerNamedLoadBalancerFromclientConfig if it doesn't exist.

I can provide more details if it is required.
Looking forward to your answers! Thanks!

[Savonitar]

Hi! Just a little friendly reminder.
Can we merge it? Or if you have some concern, we can discuss it.
Thanks!