Log cf-ray headers from CloudFlare, if available

[heckj]

This adds a replacement for the default route logging middleware from Vapor that adds in the cf-ray id, if any, from cloudflare.

This expands the logging data a bit, but gets cf-ray data exposed in the logs from the server. I'm not 100% confident how the cf-ray header is spelled and passed through, so I set this up as a low-cost experiment. My idea would be to(if this is acceptable) running this in prod for a week or two, do a log dump, and use analytics on the request logs to identify a bit more of normal-use pattern to be able to tune a rate-limiter-like cache to observe, and hopefully ameliorate, excessive bot-load, like what happened on Dec 30th.

Right now it's dumping out --nil-- in the logger metadata. More than happy to tune this to be in the log message instead of the metadata, or just not log it if the header doesn't come through. I do expect to see this in a server fronted by CloudFlare, but I don't have an easy experimental case to know for sure.

[heckj]

yeah, the --nil-- was only because I wanted to get a explicit reinforcement if I got the spelling of the header correct, and highlight where the output would be while doing the dev work - since none of that is behind CF

[finestructure]

Let's get this running on dev and we'll see how it goes.