[alias-server] Use address as parameter instead of hardcoded p2pkh and hash parameter

Summary:
T3060

We want the server to work with any arbitrary registration address, be it p2pkh or p2sh. Refactor to remove hardcoded instances of p2pkh.

Add unit test for this change in initializeWebsocket function.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13604