[ES|QL] Add CATEGORIZE+BUCKET and grouped SAMPLE examples to function reference

[charlotte-hoblik]

Closes https://github.com/elastic/docs-content-internal/issues/932

Adds tested examples to the CATEGORIZE and SAMPLE ES|QL function reference pages.

CATEGORIZE: adds a second example combining CATEGORIZE with BUCKET in the same BY clause to group log message patterns by time interval. Addresses the user question raised in the issue.

SAMPLE: adds a grouped variant showing both single-value and multivalue array return behavior in one result table. Replaces the existing employees-based example with a sample_data-based one for page-wide dataset consistency.

[elasticsearchmachine]

Pinging @elastic/core-docs (Team:Docs)

[github-actions]

🔍 Preview links for changed docs

• docs/reference/query-languages/esql/kibana/docs/functions/sample.md

[github-actions]

ℹ️ Important: Docs version tagging

👋 Thanks for updating the docs! Just a friendly reminder that our docs are now cumulative. This means all 9.x versions are documented on the same page and published off of the main branch, instead of creating separate pages for each minor version.

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