[chronik] Electrum: implement address.get_balance, get_history and listunspent

Summary:
This is just a wrapper around the scripthash.* equivalent.

Depends on D18152.

Test Plan:

./test/functional/test_runner.py chronik_electrum_blockchain

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D18153