[token-server] Tighten rate limits

Summary:
Still seeing some dedicated eCash scripters out there. Will probably need to get fail2ban going soon, but we will also need to do this.

Add rate limit object to config. Make it a param of startExpressServer, so that we can have different rate limits for the prod app and the unit tests. Include high rate limits for the tests so we do not rate limit ourselves.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D16742