[node] add forceSetArg to interface

Summary:
This commit adds a new method to the Node class to set arguments.

Partial backport of Core PR16714 - part 1 of 5
Commit 1bccf6a52d7fc08d8f605cfb2edc3277ec299c72

Test Plan:
Just make sure it still compiles: ninja
The method will be used and tested in the next commit.

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7952