Adds section to Security prebuilt ML jobs reference table

[jmikell821]

Summary

Closes elastic/security-docs#2974

Adds a "Data requirements" section to the Security anomaly detection configurations page to clarify what users need to use prebuilt ML jobs.

This addresses the core request in #2974: users can now see that they need to install one of the supported integrations listed in each job's table, and that no additional configuration is required beyond the integration's standard setup.

Changes

• Added a brief "Data requirements" section after the page intro, before the first job category
• Explicitly states that no special configuration is needed beyond standard integration setup
• Points users to the Supported Integrations column and integration documentation

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🔍 Preview links for changed docs

• reference/machine-learning/ootb-ml-jobs-siem.md

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