Expose req._startAt and req._startTime to be similar to morgan

[niftylettuce]

https://github.com/expressjs/morgan/blob/master/index.js#L500-L508

[niftylettuce]

Also https://github.com/pinojs/pino-http/blob/master/logger.js#L63 could probably be changed so that it also sets req[startTime].

[niftylettuce]

The reason I need this is because I want record the time the request was received in a log, and this is the easiest approach, since this is a timer that starts when it is received and is also the same timer used for calculation of response time.

[davidmarkclements]

Since we're modifying req objects we wanted to be as least invasive as possible we use a symbol because it's "more private".

The startTime symbol is exposed: https://github.com/pinojs/pino-http/blob/master/logger.js#L108 would that be enough to work with your end?

[niftylettuce]

This would require me to require the package and install it in my log parser, which I really didn't want to do, since the log parser I'm writing is a library to be published in npm.

Edit: And it's also a parser that works in browsers.

[niftylettuce]

Prefixing with an underscore as morgan does is probably sufficient enough.

[davidmarkclements]

We could expose it using Symbol.for, and then you can use Symbol.for('pino-http.startTime')

That way you don't have to require the package, and we don't have add more noise to the req/res objects. I'd be happy to accept a PR for altering to Symbol.for

[niftylettuce]

Closing in favor of #66 and #67