Http agent for keepAlive parameter

[lteacher]

The 'best practices' guide mentions that keepAlive can be used but this actually is a special option for axios so to include this we need to pass through the new http.Agent.

The axios reference is here in the readme

// httpAgent and httpsAgent define a custom agent to be used when performing http
// and https requests, respectively, in node.js. This allows options to be added like
// keepAlive that are not enabled by default.
httpAgent: new http.Agent({ keepAlive: true }),
httpsAgent: new https.Agent({ keepAlive: true }),