🌐 [i18n-KO] Updated ko/perf_train_special.md

[D15M4S]

What does this PR do?

Updated the perf_train_special.md file in the documentation with a Korean translation.
Thank you in advance for your review.

Part of #20179
Update of #34590

Before reviewing

• Check for missing / redundant translations (번역 누락/중복 검사)
• Grammar Check (맞춤법 검사)
• Review or Add new terms to glossary (용어 확인 및 추가)
• Check Inline TOC (e.g. [[lowercased-header]])
• Check live-preview for gotchas (live-preview로 정상작동 확인)

Who can review? (Initial)

May you please review this PR?
@jungnerd, @luckyvickyricky, @chelsseeey, @skwh54, @amo33, @maximizemaxwell

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review? (Final)