🌐 Translation of the sample site and docs into Japanese

[shin-sforzando]

Inspired by the discussion #583 and @alejandrgaspar 's great action #606, I prepared a Japanese version.
In my case, it didn't work as well as @alejandrgaspar's, translating only the samples gave me reference errors, so I translated all the Docs as well.

sample	docs

I am a native Japanese speaker and have done my best to ensure that these translations serve their purpose well and are appropriate and neutral, but I may have missed something. In particular, Japanese grammar does not separate words with spaces, which may not be compatible with Markdown notation.
To deal with this, I also used E2E testing (just takes screenshots each pages) using Playwright so I can create another PR when I feel like it.

As an aside, Australian (British) spellings such as colour and optimise made me nostalgic, reminding me of my studies in Melbourne 20 years ago.

Anyway, I hope my 10+ hours of translation work will help the community and users.
All your suggestions and help would be greatly appreciated!

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[shin-sforzando]

If you like it and decide to officially publish non-English Docs as well, you might want to specify the date and responsibility for translation.
I've also made a few corrections in the original Docs where the information was out of date.

• https://github.com/jpanther/congo/pull/618/files#diff-af5d6e3f65936b374cc18a36b879f4c3d1753a29087c19e006b9afcddd4adfa4R96
• https://github.com/jpanther/congo/pull/618/files#diff-cbdc4ea0f28373825a28194c23a99ebe3c5a9e228657c41a624971f24b698519R32
• https://github.com/jpanther/congo/pull/618/files#diff-be9bded7e4344c53392ba21d8686721122111bfb1b66dc84cd209d5d6fb0e0c0R4

[jpanther]

Thanks for this amazing contribution, @shin-sforzando! You've gone above and beyond by translating all the docs too. I'll merge this change in and I might have to start to think about how we can manage keeping the docs up to date as new features are added. I'd welcome any suggestions you might have about how this could be best achieved.

[shin-sforzando]

How about a simple annotation field on each page of the translated document to indicate which version was translated and by whom and when?