docs(components): use fallbackTag in ClientOnly examples

[HomWang]

Add 'fallbacktag', without adding 'placeholder' and 'placeholdertag'`

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• 🐞 Bug fix (a non-breaking change that fixes an issue)
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[HomWang]

props: ['fallback', 'placeholder', 'placeholderTag', 'fallbackTag'],

[pi0]

Thanks. I think we could list all available props from components reference page (<ClientOnly> missing currently)