docs: translated index page to korean (#20180)

docs: i18n: first draft of index page
docs: fix: first revision of index page
docs: i18n: missed section - supported frameworks
docs: fix: second revision of index page
review by @ArthurZucker

refactor: remove untranslated files from korean
docs: fix: remove untranslated references from toctree.yml
feat: enable korean docs in gh actions
docs: feat: add in_translation page as placeholder
docs: bug: testing if internal toc need alphabet chars
docs: fix: custom english anchor for non-alphanumeric headings
review by @sgugger

docs: i18n: translate comments on install methods in _config.py
docs: refactor: more concise wording for translations

docs/source/ko/_toctree.yml

@@ -0,0 +1,58 @@
+- sections:
+  - local: index
+    title: 🤗 Transformers
+  title: 시작하기
+- sections:
+  - local: in_translation
+    title: (번역 중)
+  title: 튜토리얼
+- sections:
+  - local: in_translation
+    title: (번역 중)
+  title: How-to 가이드
+- sections:
+  - local: in_translation
+    title: (번역 중)
+  title: 개념 가이드
+- sections:
+  - sections:
+    - local: in_translation
+      title: (번역 중)
+    title: 메인 클래스
+  - sections:
+    - isExpanded: false
+      sections:
+      - local: in_translation
+        title: (번역 중)
+      title: 텍스트 모델
+    - isExpanded: false
+      sections:
+      - local: in_translation
+        title: (번역 중)
+      title: 비전 모델
+    - isExpanded: false
+      sections:
+      - local: in_translation
+        title: (번역 중)
+      title: 오디오 모델
+    - isExpanded: false
+      sections:
+      - local: in_translation
+        title: (번역 중)
+      title: 멀티모달 모델
+    - isExpanded: false
+      sections:
+      - local: in_translation
+        title: (번역 중)
+      title: 강화학습 모델
+    - isExpanded: false
+      sections:
+      - local: in_translation
+        title: (번역 중)
+      title: 시계열 모델
+    title: 모델
+  - sections:
+    - local: in_translation
+      title: (번역 중)
+    title: 내부 유틸리티
+  title: API