Merge dev-ja into main

[Okabe-Junya]

Describe your changes

Merge dev-ja into main.
This PR includes:

• [ja] Update content/ja/cluster and nodes #3510
• [ja] Localize Platform Engineering into Japanese  #3537
• [ja] Localize Digital Certificate into Japanese #3538
• [ja] Update Service Mesh #3539
• [ja] Localize Sidecar Container into Japanese #3543

Related issue number or link (ex: resolves #issue-number)

None

Checklist before opening this PR (put x in the checkboxes)

• This PR does not contain plagiarism
  • don’t copy other people’s work unless you are quoting and contributing it to them.
• I have signed off on all commits
  • signing off (ex: git commit -s) is to affirm that commits comply DCO. If you are working locally, you could add an alias to your gitconfig by running git config --global alias.ci "commit -s".

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[seokho-son]

Some DCO issues, but let me handle it based on our repo convention.

Commit sha: 01c86ee, Author: Junya Okabe, Committer: GitHub; Expected "Junya Okabe [email protected]", but got "Junya Okabe [email protected]".
Commit sha: 5b8ae3f, Author: Junya Okabe, Committer: GitHub; Expected "Junya Okabe [email protected]", but got "Junya Okabe [email protected]".
Commit sha: 8204c57, Author: Junya Okabe, Committer: GitHub; The sign-off is missing.

[seokho-son]

LGTM!