wallet: Add HasWallets

Summary:
This is partial backport of Core PR13017 : https://github.com/bitcoin/bitcoin/pull/13017/commits/3c058fdcc8a71d17296973cb7f09e44a310df22e

Depends on D3488

Test Plan:

make check

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D3490