[cashtab] Add chronik2.fabien.cash as a backup

Summary:
This is a new chronik backend we can use as a backup.

Depends on D14102.

Test Plan: I have no idea how to test this, but I did check chronik2.fabien.cash is working using some js code.

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D14103