[backport#15006] Add option to create an encrypted wallet

Summary:
https://github.com/bitcoin/bitcoin/pull/15006/commits/662d1171d9e29964b039ba4c5bc8a2304426c003

Backport of Core PR15006

Test Plan:

ninja check
./test/functional/test_runner.py wallet_createwallet.py

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D6423