[token-server] log IP addresses of rate limited requests

Summary: To support banning IPs that make too many attempts, log when rate limited attempts occur.

Test Plan:
I ran this locally and could create the logs. npm test and confirm change only adds logs.

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D16860