[FEAT] Support `trust proxy` application setting

[asos-craigmorten]

Issue

Setup:

This issue is to support the trust proxy (and trust proxy fn) application setting, allowing users to indicate their Opine app is behind a front-facing proxy.

This issue includes the support of req.ip() and req.ips() APIs.

Details

See:

• https://expressjs.com/en/api.html#app.settings.table
• https://github.com/expressjs/express/blob/master/lib/application.js#L79
• https://github.com/expressjs/express/blob/master/lib/application.js#L91
• https://github.com/expressjs/express/blob/master/lib/application.js#L371
• https://github.com/expressjs/express/blob/master/lib/request.js#L306
• https://github.com/expressjs/express/blob/master/lib/request.js#L349
• https://github.com/expressjs/express/blob/master/lib/request.js#L366
• https://github.com/expressjs/express/blob/master/lib/request.js#L427