[Cashtab][Alias] Add chronik mock

Summary:
T3216

This diff separates out the chronik mock from D14325 and updates the registerNewAlias unit tests to be ready for websocket behaviors in D14325.

Test Plan: npm test

Reviewers: bytesofman, Fabien, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D14330