feat: Support object title for multiple language

[emjio]

Description

The title config can be translate by Object type.

title object key must be BCP-47 tag e.g. "en", "ar", or "zh-CN"

// title as string
export default defineConfig({
	integrations: [
		starlight({
			title: 'Starlight',
		}),
	],
});
// translate title by object
export default defineConfig({
	integrations: [
		starlight({
			title: {
                            en: 'Starlight',
                            'zh-CN': '星光',
                          },
		}),
	],
});

Title must have a key for the default language

// below code Will throw a error
export default defineConfig({
	integrations: [
		starlight({
			title: {
                            'zh-CN': '星光',
                          },
                         defaultLocale: 'en'
		}),
	],
});

Docs update

1. Update the type of title and add a new usage code example in docs/src/content/docs/configuration.mdx
2. Description of the new siteTitle field in docs/src/content/docs/reference/overrides.md
3. Multi-language instructions for the new title in docs/src/content/docs/guides/i18n.mdx

[changeset-bot]

🦋 Changeset detected

Latest commit: 035b38d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@astrojs/starlight	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Updated (UTC)
starlight	✅ Ready (Inspect)	Visit Preview	Apr 30, 2024 11:03am
starlight-i18n	🔄 Building (Inspect)	Visit Preview	Apr 30, 2024 11:03am

[astrobot-houston]

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[liruifengv]

Thanks for your work about this feature. I leave some suggestion.

• The title of the starlight document does not need to be changed.
• The title config need to support both string and object type.
• Update the Header's UI title in SiteTitle.astro
• You can add a changeset by run pnpm exec changeset
• You need update the docs in configuration

[astrobot-houston]

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Tracked Files

Locale	File	Note
en	guides/i18n.mdx	Source changed, localizations will be marked as outdated.
en	reference/configuration.mdx	Source changed, localizations will be marked as outdated.
en	reference/overrides.md	Source changed, localizations will be marked as outdated.

Warnings reference

Icon	Description
🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.

[delucis]

Thanks again for your patience with this PR @emjio! I just revised the documentation changes and this PR is ready to merge in our next release.

Thank you for adding this very helpful feature — we really appreciate you taking the time 🚀

Thanks also to @liruifengv for championing and helping review this idea 💖

[liruifengv]

LGTM. Congratulations！