Singular data tests can now be documented

[dbeatty10]

Resolves #6132
Originally #6147

What are you changing in this pull request and why?

The description property is available for singular data tests beginning in dbt v1.9, and this PR highlights how singular tests can now be documented.

🎩 Previews

• description
• docs-paths
• documentation placement

Additional information

Opened #6193 since we don't have documentation how to add a description for the Jinja macro associated with custom generic tests. This follow-up will allow us to consider the description of both generic and singular data tests in context of each other.

Checklist

• I have reviewed the Content style guide so my content adheres to these guidelines.
• The topic I'm writing about is for specific dbt version(s) and I have versioned it according to the version a whole page and/or version a block of content guidelines.
• Wait until [Round 2] Fix #9005: Allow singular tests to be documented in properties.yml dbt-core#10792 is merged
• Add a note to the prerelease version Migration Guide

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Name	Status	Preview	Updated (UTC)
docs-getdbt-com	✅ Ready (Inspect)	Visit Preview	Oct 1, 2024 3:45pm

[mirnawong1]

small tweak!

[graciegoheen]

@dbeatty10 @mirnawong1 I'm realizing this doesn't have a release note - should we add one?

[mirnawong1]

good point and have created a release note PR here: #6227