Make timeout on clj-http-client configurable

Earlier today I found myself wanting to increase the timeout on the proxy the classifier UI uses, because the classifier API was taking too long to respond. However, the proxying is done by ring-middleware which simply uses clj-http-client to make requests, and after talking with preben I learned that that's not currently configurable.

The ability to configure this timeout would be extremely useful for support situations where slow responses are an issue.

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The work for this issue ultimately involved exposing two new client configuration settings:

connect-timeout-milliseconds - maximum number of milliseconds that the client will wait for a connection to be established.

socket-timeout-milliseconds - maximum number of milliseconds that the client will allow for no data to be available on the socket before closing the underlying connection, 'SO_TIMEOUT' in socket terms.

Risk assessment: High (automated test needed)
Probability: Medium (effects users needing to adjust timeout)
Severity: High (No work around available)