[herald] Refactor handleBlockConnected to support multiple api calls later

Summary:
T2972

Depends on D13620

Refactor handleBlockConnected so that chronik API call has its own try...catch block

Future API calls will also need their own try...catch blocks

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13622