feat: add log file support

[jokresner]

This PR adds two new flags to enable logging to a file. See #1716

[github-actions]

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[simskij]

I like this, and would be happy to merge it after one change: enabling logging to a file should still log to stdout as well.

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (76f9cea) 70.55% compared to head (8ea89ce) 70.56%.

❗ Current head 8ea89ce differs from pull request most recent head 07d200b. Consider uploading reports for the commit 07d200b to get more accurate results

Files	Patch %	Lines
internal/flags/flags.go	63.63%	7 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1813      +/-   ##
==========================================
+ Coverage   70.55%   70.56%   +0.01%     
==========================================
  Files          26       26              
  Lines        2493     2511      +18     
==========================================
+ Hits         1759     1772      +13     
- Misses        633      638       +5     
  Partials      101      101              

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[jokresner]

Sorry for my late replay. I've added a multi writer to support both outputs.

[IvanRibakov]

@simskij Could you please take another look at this PR?