[ecash-herald] Send daily summaries to the main chat

Summary:
Depends on D17724

Right now these are manually forwarded. We might as well have the bot send them there, too.

Test Plan: npm test, I will need to update the CI, add the bot to the chat. Won't really know it works until the msg is in main.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D17725