[backport] RPCAuth Detection in Logs

Summary:
dae0d13bbb710346a8f4c8ecdf96937283e470df RPCAuth Detection in Logs (Linrono)

Pull request description:

This adds a log entry for when RPCAuth is detected.
This keeps everything working as it currently is. I suppose it could be added as a nested if to also stop the creation of the cookie file if this would be wanted.

This is a backport of Core PR13118

Test Plan:

ninja check

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5688