feat: Add client observability enhancement docs

[FAWC438]

What is the purpose of the change

The main purpose of this PR is to migrate the content of #402 to the new front-end framework branch.

Note that this PR should NOT be merged now, because the relevant code functions are still being adjusted and are not yet guaranteed to be available. These documents may change at any time. I will notify the community here when the document is finalized .

Unlike the previous framework, the new front-end framework does not seem to provide guidance on submitting new markdown files. So, I referenced the format of previous commit history to create this PR. Also, do I have to manually create the English version of the document, or are there any translation plugins available for the new front-end framework? The community can always give me suggestions on the format of my submissions.

Brief changelog

• Nacos 客户端可观测性能力使用文档
• Nacos 客户端可观测性指标文档

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[heimanba]

麻烦可以PR到 develop-astro-nacos分支