fix(backend): メールアドレスの形式が正しくなければ以降の処理を行わないように

[sakuhanight]

What

メールアドレスバリデーションの追加

Why

予期しないメールアドレスの入力が可能だった

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

[sakuhanight]

#15056 からバリデーションの追加だけもってきました

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 10 lines in your changes missing coverage. Please review.

Project coverage is 42.13%. Comparing base (e2a55e2) to head (ba52862).
Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/backend/src/core/EmailService.ts	0.00%	7 Missing ⚠️
packages/backend/src/core/UtilityService.ts	62.50%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #15320       +/-   ##
============================================
+ Coverage    14.57%   42.13%   +27.55%     
============================================
  Files          770     1609      +839     
  Lines        68497   161803    +93306     
  Branches      1305     4087     +2782     
============================================
+ Hits          9982    68168    +58186     
- Misses       58086    93187    +35101     
- Partials       429      448       +19     

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[github-actions]

このPRによるapi.jsonの差分
差分はありません。
Get diff files from Workflow Page

[Sayamame-beans]

恐らく良いのではないでしょうか
changelogの追加はあっても良いかもしれません

[mi-gh-maintainer]

Thank you 🙏