channel_detail_infoにチャンネルURLのコピーボタンを追加

[Npepperlinux]

Resolve #598
チャンネルのリンクをコピーするボタンを追加しました。

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 52.94118% with 8 lines in your changes missing coverage. Please review.

Project coverage is 27.72%. Comparing base (8512cea) to head (c9aae31).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
lib/view/channels_page/channel_detail_info.dart	52.94%	8 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #680      +/-   ##
===========================================
- Coverage    27.73%   27.72%   -0.02%     
===========================================
  Files          312      312              
  Lines        16296    16304       +8     
===========================================
  Hits          4520     4520              
- Misses       11776    11784       +8     

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[Npepperlinux]

何故linkアイコンではなくcopyアイコンを選んだんだ…？