Update docs based on agent experience review - #91

Running Vale across on the following files affected by this PR:

- api-reference/client-libraries.mdx
- api-reference/introduction.mdx
- es/api-reference/client-libraries.mdx
- es/api-reference/introduction.mdx
- es/getting-started/introduction.mdx
- es/getting-started/quickstart.mdx
- getting-started/introduction.mdx
- getting-started/quickstart.mdx
- snippets/metric-change-request-block.mdx
- snippets/metric-change-response-block.mdx
- api-reference/errors.mdx
- es/api-reference/errors.mdx
- es/getting-started/production-checklist.mdx
- getting-started/production-checklist.mdx
- snippets/verified-first-event.mdx

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