[chronik hotfix] use chronik.be.cash servers for live apps

Summary: End app downtime with temp move to chronik.be.cash/xec, which is live.

Test Plan: Confirm url entered correctly into config

Reviewers: #bitcoin_abc, PiRK, Fabien

Reviewed By: #bitcoin_abc, PiRK, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14858