[ecash-telegram-bot] MVP example telegram bot using chronik to announce blocks found

Summary:
T2972

Example app Telegram bot to be used in a future dev blog post

MVP bot will announce newly found blocks to a Telegram channel

Test Plan:
If you like, create your own bot and channel, cp secrets.sample.js secrets.js, update the bot info, and node index.js. Wait for a new block to be found and note that the msg is broadcast to the channel you entered in secrets.js

Otherwise it's ok to just check out the code and green/suggest changes. This isn't critical infra and future diffs will improve the functionality.

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D13234