[tg bot] change msg format from markdown to html

Summary:
T2972

Depends on D13280

In preparation for supporting op_return msg parsing, convert app from sending 'markdown' style telegram msgs to 'html' style. In the Telegram API, it's easier to clean strings for html format (only need to replace 3 special characters vs several in markdown)

Test Plan:
npm run test
npm run msgs and all send, look ok

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D13281