[alias-server] Check avalanche isFinalBlock in handleBlockConnected

Summary:
T3060

Depends on D13633

Check isFinalBlock status. If block is not final, do not update aliases in handleBlockConnected.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13634