[ecash-herald] Log success msgs by blockheight

Summary:
T2972

Depends on D14175

Log blockheight success msg if msg(s) successfully sent for a given blockheight

Useful for reviewing logs and seeing if any blocks were missed

Test Plan: Confirm change only adds a log that only happens if an optional param is passed, npm test still good

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14176