docs: add unplugin-vue-i18n setting for petite-vue-i18n

[kazupon]

related #1965

[cloudflare-workers-and-pages]

Deploying vue-i18n-next with    Cloudflare Pages

Latest commit:	3b06c19
Status:	✅  Deploy successful!
Preview URL:	https://a2d11fbc.vue-i18n-next.pages.dev
Branch Preview URL:	https://docs-petite-1.vue-i18n-next.pages.dev

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[pkg-pr-new]

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@intlify/core

pnpm add https://pkg.pr.new/@intlify/core@1968

@intlify/core-base

pnpm add https://pkg.pr.new/@intlify/core-base@1968

@intlify/devtools-types

pnpm add https://pkg.pr.new/@intlify/devtools-types@1968

@intlify/message-compiler

pnpm add https://pkg.pr.new/@intlify/message-compiler@1968

petite-vue-i18n

pnpm add https://pkg.pr.new/petite-vue-i18n@1968

@intlify/shared

pnpm add https://pkg.pr.new/@intlify/shared@1968

vue-i18n

pnpm add https://pkg.pr.new/vue-i18n@1968

@intlify/vue-i18n-core

pnpm add https://pkg.pr.new/@intlify/vue-i18n-core@1968

commit: 3b06c19