[chronik.e.cash] Use array implementation in examples

Summary: We can initialize with a string, but array is best practice. Use it everywhere.

Test Plan: grep -r 'new ChronikClient' docs/ and make sure you got them all

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D16777