cli: use GetWalletBalances() functionality for -getinfo

Summary:
and replace GetBoolArg with IsArgSet as we only want
to know if the arg is passed; we do not need the value.

This is a backport of Core PR18594 [4/6]
https://github.com/bitcoin/bitcoin/pull/18594/commits/afce85eb994384246e455b766549c3206cb059e0

Depends on D9239

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9240