[alias-server] Get block height in handleBlockConnected

Summary:
T3060

Depends on D13630

Get tipHeight in handleBlockConnected function for later use in processing valid aliases

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13631