Use Version 2 config for sqlc.yaml

[dmjb]

This makes it easier to reuse examples from the documentation.

Summary

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Fixes #(related issue)

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• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
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Review Checklist:

• Reviewed my own code for quality and clarity.
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• Updated any affected documentation.
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[jhrozek]

make gen doesn't produce any diff -> good

[coveralls]

coverage: 53.056% (+0.004%) from 53.052%
when pulling d3909a5 on sqlc-2.0-config
into a441c32 on main.