refactor(logger) : Deprecate the Discord, Slack structures, and send logs via a Handler.

[seipan]

resolve : #30
Originally, we had structures named Discord and Slack, each containing a webhook URL, and used these structures to switch between slack and discord types to send logs. However, this approach is cumbersome from the perspective of custom handlers, so we will be doing a comprehensive refactoring. I consider this to be a long-term task, and we will take our time to ensure the previous functionalities are preserved.

[codecov]

Codecov Report

Attention: 59 lines in your changes are missing coverage. Please review.

Comparison is base (8440a71) 43.14% compared to head (81110a4) 43.94%.
Report is 2 commits behind head on main.

Files	Patch %	Lines
logger.go	37.50%	25 Missing ⚠️
option.go	45.94%	20 Missing ⚠️
webhook.go	53.33%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #33      +/-   ##
==========================================
+ Coverage   43.14%   43.94%   +0.80%     
==========================================
  Files           5        4       -1     
  Lines         394      314      -80     
==========================================
- Hits          170      138      -32     
+ Misses        222      174      -48     
  Partials        2        2              

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