[Docs] Clean up v1/metrics.md

[windsonsea]

Performed these minor actions:

• try to improve and fix some grammar issues
• fix consistency issues on style
• fix a 1-2-3 list
• put link text and its url onto a single line, so the color will be changed when you edit it in an IDE

No any meaning changed.

docs/design/v1/metrics.md

[gemini-code-assist]

Code Review

This pull request provides a nice cleanup of the metrics.md design document, improving grammar, style consistency, and link formatting. The changes enhance readability. I've identified one issue with markdown formatting where paragraphs under list items are indented with 4 spaces, which would incorrectly render them as code blocks. I've suggested changing this to a 2-space indent to ensure correct rendering as paragraphs.

[hmellor]

Thank you for this cleanup!

[github-actions]

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