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]

Thanks so much for opening your first PR here!

[CLAassistant]

All committers have signed the CLA.

[AlliotTech]

It appears I don't have permission to set the milestone to pass the pre-check.

[coveralls]

Pull Request Test Coverage Report for Build 11648981603

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%

---

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

---

💛 - Coveralls

[AlliotTech]

Hi, I would like to follow the progress of this PR. Will this PR be merged in the next release? Are there any changes that need to be made or optimized?

[stevenjoezhang]

@AlliotTech Thank you for your patience, this pull request will be merged

[welcome]

Congrats on merging your first pull request here! 🎉 How awesome!