🌐 [i18n-KO] Translated `cache_explanation.md` to Korean (#39535)
* update: _toctree.yml
* docs: ko: cache_explanation.md
* feat: nmt draft
* fix: apply yijun-lee's comments
* fix: apply 4N3MONE's comments
* docs: update cache_position
* docs: update cache-storage-implementation
* update: add h2 tag in cache-position
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Co-authored-by: taehyeonjeon <xogus294@gmail.com>