docs(seed-docs): add avatar group options

[yoonk2]

• Anatomy 이미지 기본 옵션인 top item=last item 배리언트 이미지로 변경
• 옵션 가이드라인 추가
  • Size
  • Top Item
  • Limit
• xxlarge, xlarge 사이즈 옵션 제거
• Excess Count typography style 변경

[changeset-bot]

⚠️ No Changeset found

Latest commit: 5f4c5a5

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[github-actions]

Deploy Seed Docs Alpha Pages / Deploy Seed Docs (push) CI가 성공적으로 끝나면 해당 링크로 이동해서 preview를 확인해요 -> https://dash.cloudflare.com/aad5c82543cd1f267b89737d0f56405e/pages/view/seed-design