[alias-server] Implement better chronik mock

Summary:
T3060

As demands on mocked chronik become more sophisticated, the mock needs to be improved. This implements the same chronik mock implemented in D13627 on ecash-herald.

A task is open to create a standalone library for chronik mock, which needs its own README, unit tests, etc.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13629