BasicTestingSetup: Add ArgsManager.
Summary:
This is a backport of core#21244 [5/8]
https://github.com/bitcoin/bitcoin/pull/21244/commits/511ce3a26b3b78e14acd0d85496b5422a236cf63
Depends on D10753
Test Plan: ninja check
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Subscribers: Fabien
Differential Revision: https://reviews.bitcoinabc.org/D10752