Update service_unit_quantity definition

[eldon-tuva]

Describe your changes

Please include a summary of any changes.

Update yml docs for service_unit_quantity to match change in PR #431

How has this been tested?

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Checklist before requesting a review

• [ ] I have added at least one Github label to this PR (bug, enhancement, breaking change,...)
• [ ] My code follows style guidelines
• [ ] (New models) YAML files are categorized by sub folder and models listed in alphabetical order
• [ ] (New models) I have added a config to each new model to enable it for claims and/or clinical data
• [ ] (New models) I have added the variable tuva_last_run to the final output
• [ ] (Optional) I have recorded a Loom to explain this PR

Package release checklist

• [ ] I have updated dbt docs
• [ ] I have updated the version number in the dbt_project.yml

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