[chronik] Electrum: Use TLS as a default protocol

Summary: This changes the default for -chronikelectrumbind to use the TLS (:s) protocol. Secure as a default is a better option, and this match the default ports on Fulcrum also.

Test Plan:

./test/functional/test_runner.py chronik_electrum_*

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D18112