feat: allow specifying noindex for robots

[AlliotTech]

PR Checklist

• The changes have been tested (for bug fixes / features).
• Docs in NexT website have been added / updated (for features).(ref: docs: update front-matter.md theme-next-docs#131)

PR Type

• Bugfix.
• Feature.
• Improvement.
• Code style update (e.g. formatting, linting).
• Refactoring (no changes to functionality and APIs).
• Documentation.
• Translation.
• Other... Please describe:

What is the current behavior?

Issue resolved:

What is the new behavior?

• allow add noindex head meta.(ref: block-indexing)

How to use?

Add in page frontmatter:

noindex: true

[welcome]

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[CLAassistant]

All committers have signed the CLA.

[AlliotTech]

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[coveralls]

Pull Request Test Coverage Report for Build 11358856685

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 97.446%

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Totals
Change from base Build 10956680841:	0.0%
Covered Lines:	400
Relevant Lines:	405

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💛 - Coveralls