[alias-server] [p10] Store blockheight in parsed alias txs

Summary:
T2922

Depends on D13111

Store blockheight in parsed alias txs. This is necessary to determine the valid alias in cases where the same alias has been registered multiple times.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D13112