Add request ID to nginx and docassemble logs

[rajeswari1301]

This gives every request its own ID starting at nginx, so the logs it produces can be traced together instead of by timestamp.
I tested confirming the ID shows up correctly for normal page loads and background tasks alike, and that a fake client-sent ID gets overridden by nginx's real one rather than trusted.

I didn't wire the ID directly into background task logs, since Celery skips our whole logging setup there, and session ID plus a user identifier in the log line covers what's actually needed for that case, so that's what this does instead. And left nginx's own access log without the ID for now, I couldn't find a reason that needed it.

Addresses #72

[BryceStevenWilley]

Tested, looks good, request id does get added as expected!

The only issue I found was the fact that I don't think the request id shows up in the uwsgi.log or access.log, and I think that was a goal of this id (so we could cross correlate between logs). Could probably go in in another PR (I think adding log_format to nginx.conf in this repo is what we want (https://docs.nginx.com/waf/logging/access-logs/)).