allow only logging to stderr with minloglevel

[eagleoflqj]

Pull request

Issue tracker

Fixes will automatically close the related issue

Fixes #727

Feature

Before:
If app_name not provided, only log to stderr, min_log_level doesn't work at all.
If app_name provided, log to both stderr and file (if log_dir not provided, use temporary dir).

After:
If app_name provided and provide log_dir as empty string, log only to stderr with min_log_level working.

Unit test

• Done

Manual test

• Done

Code Review

1. Unit and manual test pass
2. GitHub Action CI pass
3. At least one contributor reviews and votes
4. Can be merged clean without conflicts
5. PR will be merged by rebase upstream base

Additional Info