[ko] Add Korean translation for index.adoc

[smileboy0014]

Summary

This PR adds an initial Korean translation of the index.adoc file, which serves as the entry point for the Spring Framework reference documentation.

Motivation

As a Spring developer based in South Korea, I’ve found it somewhat challenging to navigate the documentation due to the lack of a Korean version. Given the large and active community of Spring developers in Korea, I believe that having a localized version of the documentation will make it significantly more accessible and beneficial to others.

Future Plans

This translation is the first step in my broader goal of contributing Korean translations for key parts of the Spring documentation. I plan to progressively translate more sections, starting with core modules, in order to make Spring more approachable for Korean-speaking developers.

If this PR is welcome, I’d like to contribute more documents progressively. Please let me know if there’s any direction/preference for the Korean translations.

Thank you for your consideration!

[bclozel]

Thanks for the proposal @smileboy0014 but we don't have the bandwidth nor the skills to maintain a multi-language reference documentation. Hopefully automated translation or community-maintained docs can help. Our official documentation is evolving too fast for us to maintain variants. See #23786 #9008 for similar requests.