[Cashtab] Broadcast alias registration txs per latest spec

Summary:
T3060

Configure Cashtab to broadcast alias registration txs according to revised spec for v0 alias registration txs

Note: For now, only support registering an alias to the active Cashtab wallet. Will add support for registering arbitrary other addresses (including p2sh addresses) later.

Note: This will only impact prod app if aliasEnabled is set to true in Ticker.js

Test Plan: npm test

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13845