get config via ChainstateManager when it is reachable
Summary:
This is another step toward deglobalizing the Config.
This diff does not deal with the fuzzer, this will be split in another diff.
Depends on D16116
Test Plan: ninja all check-all bench-bitcoin
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D16117