Resolve "对前端安全 review 的支持"

What does this MR do and why?

• 在 event.rb 中添加 has_frontend_label? 和 has_backend_label? 方法
• 修改 SecurityReviewDisapprove 和 SecurityReviewReady 的 valid_security_reviewer_members 方法
• 修改相应的 spec

Closes #133 (closed)

related team-members MR: https://jihulab.com/jihulab/engineering/team-members/-/merge_requests/112