[alias-server] replace optionalMocks param with mocked instance of chronik

Summary:
T3060

Depends on D13599

Replace passed mocks param with a mocked instance of chronik that returns mock data in expected chronik format

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13602