detect-secrets-hook read file list from a file, to allow use of exit code about detect-secrets

[gpflaum]

Upgrading from detect-secrets 1.4 to 1.5 is causing problems for us because detect-secrets-hook 1.5 updates the baseline file even if no new secrets are found. It returns exit code 3 in this case, causing failures in our build pipelines. I'd like to ignore that case, but it's difficult to get the exit code when using xargs.

[gpflaum]

Updated the description with an additional problem that can happen when using xargs and scanning very many files.