Add verified queries (draft)

[rlittle08]

Extends the spec for new section - verified_queries.

What will this be used for?

• For humans: documenting approved query patterns within a semantic model
• For AI: In tools like Cortex Analyst in Snowflake, will be directly used for query generation by AI tools

Why does it warrant inclusion in this spec?

• For both use cases listed above, example queries are universally helpful
• Having a namespace defined in the standard supports interoperable use, and allows data vendors to share proper query patterns with multiple downstream applications (AI or otherwise), in one place