[chronik apps] Revert back to chronik.fabien.cash as primary chronik backend

Summary:
Following yesterday's chronik outage, we are ready to move back to ABC-hosted chronik as the primary backend.

A task has been created to support redundant chronik instances in the chronik-client library to prevent the need for manual swaps in the future.

Test Plan: Confirm all apps impacted by D14089 and D14090 have been reverted back to https://chronik.fabien.cash as the primary backend

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14096