[alias-server] implement new db functions in handleBlockConnected to fetch and store aliases

Summary:
T3060

Modify handleBlockConnected function in events.js to update the database with aliases.

Modify mocks and unit tests for new logic.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13707