Modify log config to write errors to a separate log file

[nvkevlu]

Modify log config to write errors to a separate log file in addition to log.txt.

Description

Modify log config to write errors to a separate log file in addition to log.txt. I think this covers all the places we provide a default log config and this will enable future work for the error logs to be aggregated for reporting and downloading.

Updated nvflare/private/fed/utils/fed_utils.py to add an error log file to write errors to using the configuration of the error file handler based on the errorFileHandler in log.config.

Types of changes

• [x] Non-breaking change (fix or new feature that would not break existing functionality).
• [ ] Breaking change (fix or new feature that would cause existing functionality to change).
• [ ] New tests added to cover the changes.
• [ ] Quick tests passed locally by running ./runtest.sh.
• [ ] In-line docstrings updated.
• [ ] Documentation updated.

[yanchengnv]

@IsaacYangSLA please review. Thanks!

[nvkevlu]

/build

[YuanTingHsieh]

/build