Allow custom client options for clients

[jBonoraW]

We want to have a way to set custom options for clients, in order to being able to instead using public connection for Gcloud api use the interconnect network.

The aim is improving the resilience of the applications using rele in a Gcloud environment, in addition speed is going to be improved, because Cloud Interconnect extends your external network to the Google network through a high-availability, low-latency connection.