[token-server] Improve logging

Summary:
Because token-server runs in a docker container, the IP logging I set up from local testing does not actually work. It just logs the IP address of the server itself.

Looking at this as a solution: https://stackoverflow.com/questions/10849687/express-js-how-to-get-remote-client-address

Test Plan: Check logs in prod. May need to iterate and improve here with how the app is deployed.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D16703