[ecash-herald] Support daily summary msgs

Summary:
Send a daily summary msg every 144 blocks

ecash-herald in its current form is a useful reference or alert system for power users. I think we could get more impact from higher level summaries of daily on chain activity. This is more representative of eCash KPIs.

Start with a simple template. Going forward, will be an editorial question what we should be tracking.

Test Plan:
npm test, review msg sample

after updating diff:

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D16911