[Cashtab] Migrate to ABC chronik instance

Summary:
T2477

Chronik implementation so far has always had a fallback in case the server is down. If the websocket connection does not work, the app will update with regular API pings as before.

The next batch of changes will begin to replace the API functionality with chronik. Hence, ABC should control the infra behind Cashtab. This way upgrades to Chronik may be tested before being implemented in Cashtab.

Test Plan: npm start, send and receive txs, note that incoming tx notifications work and wallet balance adjusts

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D11732