[ecash-agora] Support for ALP relist

Summary: Add a new relist method to AgoraOffer. This is useful for updating the terms of an existing offer without canceling it in one tx and then recreating it in another tx. For example, this method would be useful in updating the price of an existing offer.

Test Plan: npm test, CI test

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D18847