[ja] Localize index page

[ymotongpoo]

Docs PR Checklist

• This PR is for a documentation page whose authoritative copy is in the
  opentelemetry.io repository.

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Preview: https://deploy-preview-4580--opentelemetry.netlify.app/ja/

[svrnm]

Thanks @ymotongpoo, can you ask someone who is also a native Japanese speaker to provide a review?

@chalin does this PR everything you need to add Japanese as a language to the website?

[ymotongpoo]

@shirou @katzchang can either of you review the JA translation? The volume is pretty small.

[chalin]

Thank you for this PR!

As I mentioned during the Comms meeting yesterday, I'll get to this as soon as I can. There's an i18n feature I may want to put into place first.

That being said, there are rebase conflicts. Please rebase and force push and I'll take a look after. I tried rebasing myself, but I'm not qualified to resolve the merge conflicts because I don't understand Japanese 😄.

[chalin]

While I still can't rebase, I have made all the necessary fixes. For a preview, see https://deploy-preview-4580--opentelemetry.netlify.app/ja/

IMHO, this is good to merge.

[chalin]

We'll need a Japanese translation of "The OpenTelemetry Project Site" to put in these lines. No rush, it can be handled in a followup PR.

[ymotongpoo]

@chalin Thank you for your review and I rebased and force pushed my branch to resolve conflicts. I also added metadata in Hugo config for Japanese pages.

[svrnm]

https://opentelemetry.io/ja/ 🎉