i18n(ja): Update configuration.md

[morinokami]

What kind of changes does this PR include?

• Changes or translations of Starlight docs site content

Description

• Update configuration.md
  • Include built-in UI translation for regional docs #475
  • Add Instagram icon #499

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Latest commit: e4572c2

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[delucis]

LGTM! Thank you @morinokami 🚀