fix(backend): カスタム絵文字の一括インポートをした時にHTTPプロキシの除外設定が効かないのを修正

[samunohito]

What

DownloadServiceによるファイル取得時に、HTTPプロキシの除外設定に従って適切なhttpAgent/httpsAgentを使用するようにしました。

Why

fix #8766

Additional info (optional)

元issueのSteps to Reproduceどおりに操作して問題の発生を確認
↓
修正後のソースで同じ手順で捜査してインポートが動作するのを確認

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Add story of storybook
• (If needed) Update CHANGELOG.md
• (If possible) Add tests

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 52.38095% with 20 lines in your changes missing coverage. Please review.

Project coverage is 42.16%. Comparing base (39c487e) to head (4698ae3).
Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/backend/src/core/HttpRequestService.ts	55.00%	16 Missing and 2 partials ⚠️
packages/backend/src/core/DownloadService.ts	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #15431      +/-   ##
===========================================
- Coverage    42.18%   42.16%   -0.02%     
===========================================
  Files         1610     1610              
  Lines       162118   162151      +33     
  Branches      4057     4043      -14     
===========================================
- Hits         68387    68370      -17     
- Misses       93292    93308      +16     
- Partials       439      473      +34     

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[mi-gh-maintainer]

Thank you 🙏