fix: EmailServiceでインラインスタイルを適用するように

[1673beta]

What

EmailService中のHTMLにインラインCSSを適用するように

before

after

Why

close #8888

Additional info (optional)

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]

このPRによるapi.jsonの差分

差分はこちら

Get diff files from Workflow Page

[codecov]

Codecov Report

Attention: Patch coverage is 7.14286% with 13 lines in your changes missing coverage. Please review.

Project coverage is 39.64%. Comparing base (a18a6ac) to head (1cd0cdb).
Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/backend/src/core/EmailService.ts	7.14%	13 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #14600      +/-   ##
===========================================
- Coverage    41.47%   39.64%   -1.83%     
===========================================
  Files         1545     1541       -4     
  Lines       197945   192213    -5732     
  Branches      3568     2491    -1077     
===========================================
- Hits         82104    76212    -5892     
- Misses      115247   115437     +190     
+ Partials       594      564      -30     

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[syuilo]

🙏🏿🙏🏿🙏🏿

[kakkokari-gtyih]

Changelogがいりそう（後でやっておく）

[1673beta]

お願いします🙇(忘れてた)