Expose retry / request timeout information via configuration

As a IT manager with a flakey connection, I want to configure high request timeouts and retries, so that I can ensure that the card client is able to fetch the data required rather than failing when a timeout occurs.

An IT manager has confirmed that he's seen the cardclient fail a few times with requests timing out - this is likely due to network latency issues.

The card client does by default retry requests and sets a fairly high request timeout, however it would be useful to expose these settings through the config, to allow people using the card client to configure higher timeouts.

As part of this we should update the readme with details of how these settings can be used.