Use the actual config in the RPC console

Summary: The Qt RPC console uses a default config and causes the RPC to behave slightly differently than they do from bitcoind. This diff fixes that by forwarding the config at execution time.

Test Plan:

ninja all check-all

On the RPC console, run getnewaddress and check it returns an ecash address (was a legacy one before the patch).

Reviewers: #bitcoin_abc, tyler-smith

Reviewed By: #bitcoin_abc, tyler-smith

Subscribers: Mengerian

Differential Revision: https://reviews.bitcoinabc.org/D11370