Add Korean translations (ko) for Lesson 19-21

[IsuminI]

We have added Korean translations for lesson 19 to lesson 21.
This is my first time creating a Pull requests, so it might not be perfect. Thank you for your understanding.

[github-actions]

👋 Thanks for contributing @IsuminI! We will review the pull request and get back to you soon.

[IsuminI]

@microsoft-github-policy-service agree

[github-actions]

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File Full Path	Issues
04-prompt-engineering-fundamentals/README.md	# Link Line Number 1 https://python.langchain.com/docs/modules/model_io/prompts/prompt_templates/?WT.mc_id=academic-105485-koreyst 284
04-prompt-engineering-fundamentals/translations/ko/README.md	# Link Line Number 1 https://python.langchain.com/docs/modules/model_io/prompts/prompt_templates/?WT.mc_id=academic-105485-koreyst 273
04-prompt-engineering-fundamentals/translations/tw/README.md	# Link Line Number 1 https://python.langchain.com/docs/modules/model_io/prompts/prompt_templates/?WT.mc_id=academic-105485-koreyst 278
04-prompt-engineering-fundamentals/translations/ja-jp/README.md	# Link Line Number 1 https://python.langchain.com/docs/modules/model_io/prompts/prompt_templates/?WT.mc_id=academic-105485-yoterada 298
04-prompt-engineering-fundamentals/translations/cn/README.md	# Link Line Number 1 https://python.langchain.com/docs/modules/model_io/prompts/prompt_templates/?WT.mc_id=academic-105485-koreyst 271
04-prompt-engineering-fundamentals/translations/pt-br/README.md	# Link Line Number 1 https://python.langchain.com/docs/modules/model_io/prompts/prompt_templates/?WT.mc_id=academic-105485-koreyst 277
17-ai-agents/translations/tw/README.md	# Link Line Number 1 https://python.langchain.com/docs/modules/agents/?WT.mc_id=academic-105485-koreyst 41
16-open-source-models/README.md	# Link Line Number 1 https://opensource.org/osd?WT.mc_id=academic-105485-koreyst 15
16-open-source-models/translations/tw/README.md	# Link Line Number 1 https://opensource.org/osd?WT.mc_id=academic-105485-koreyst 15

[scorpion20144]

hi
how are you?
i am from IRAN
I am happy to meet you