[ecash-telegram-bot] Add etoken and genesis tx info in block msgs

Summary:
T2972

Add genesis tx info to Telegram msgs for new block found

Also adds numerous improvements to support this complication, including unit tests and mock generation

Test Plan:
Review unit tests and npm test
node index.js, send some etoken txs and/or mint an etoken, confirm bot msg correctly describes activity of the block

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D13263