[ecash-herald] Rename ecash-telegram-bot to ecash-herald

Summary:
T2972

Initialize new top level apps/ folder and populate it with the telegram bot, renamed to ecash-herald

Test Plan: cd apps/ecash-herald and npm test, all pass

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13558