Make [KO],[ES], [PT] translations publishable

[ilyaspiridonov]

Made Korean, Spanish and Portuguese translations publishable:

• updated config.yaml to include the three languages in the build;
• added toc.yaml for each of the three languages. Section names are Google-translated.

NB Bengali and Chinese can not be added until #1602 is resolved.

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[clausia]

To publish each language, I thought we should follow this guide
https://github.com/Qiskit/platypus/blob/main/translations/release_guide.md

On the other hand, the translated toc.yaml file must be proofread before merging, isn't it?

[ilyaspiridonov]

Thank you @clausia, this PR basically does what is described in the Release Guide.
This is intended to lower the bar for the community to make new translated textbooks publishable (as right now the project has some notebooks available in 5 languages, but none of those have made it to the production release yet ;)

Regarding proofreading - good point, I used Google Translate here as the initial translation, and the community can later improve if necessary (or review here in this PR).
The translations are only the section titles (not textbook titles and TOC items, as those are parsed directly from the translated textbooks).

[vabarbosa]

@ilyaspiridonov thank you for getting this started. i switched the base branch to feat/translations (instead of main) that way we can set up/generate preview URL with the changes before pushing to main.

[0sophy1]

@ilyaspiridonov Thank you so much..!