feat(contrib/config): use key file extension as format & config load log

[Windfarer]

fixes of #1610

[codecov-commenter]

Codecov Report

Merging #1619 (4857a66) into main (fcd9351) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1619      +/-   ##
==========================================
+ Coverage   81.50%   81.51%   +0.01%     
==========================================
  Files          78       78              
  Lines        3412     3414       +2     
==========================================
+ Hits         2781     2783       +2     
  Misses        432      432              
  Partials      199      199              

Impacted Files	Coverage Δ
config/config.go	55.84% <100.00%> (+1.17%)	⬆️

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