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/_config.py

@@ -0,0 +1,14 @@
+# docstyle-ignore
+INSTALL_CONTENT = """
+# Transformers 설치 방법
+! pip install transformers datasets
+# 마지막 릴리스 대신 소스에서 설치하려면, 위 명령을 주석으로 바꾸고 아래 명령을 해제하세요.
+# ! pip install git+https://github.com/huggingface/transformers.git
+"""
+
+notebook_first_cells = [{"type": "code", "content": INSTALL_CONTENT}]
+black_avoid_patterns = {
+    "{processor_class}": "FakeProcessorClass",
+    "{model_class}": "FakeModelClass",
+    "{object_class}": "FakeObjectClass",    
+}