🌐 [i18n-KO] Translated `trainer.md` to Korean (#32260)

* docs: ko: ko-trainer

* feat: nmt draft

* fix: manual edits

* fix: manual edits

* fix: glossary

* fix: glossary

* Apply suggestions from code review
Co-authored-by: Jinuk <45095330+JinukHong@users.noreply.github.com>
Co-authored-by: SeongWooChoi <46990061+nuatmochoi@users.noreply.github.com>

---------
Co-authored-by: Jinuk <45095330+JinukHong@users.noreply.github.com>
Co-authored-by: SeongWooChoi <46990061+nuatmochoi@users.noreply.github.com>

docs/source/ko/_toctree.yml

@@ -117,8 +117,8 @@
     title: 사용자 정의 모델 공유하기
   - local: chat_templating
     title: 챗봇 템플릿 익히기
-  - local: in_translation
-    title: (번역중) Trainer
+  - local: trainer
+    title: Trainer 사용하기
   - local: sagemaker
     title: Amazon SageMaker에서 학습 실행하기
   - local: serialization