Minor updates to yml documentation for Core and Chronic Conditions

[sarah-tuva]

Describe your changes

• Document missing column for observation in core and integration_tests.
• Clean up core yml
• Clarify chronic condition columns

How has this been tested?

Ran dbt build && dbt docs generate && dbt docs serve.

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Checklist before requesting a review

• I have updated the version number in dbt_project.yml file to reflect the release number of this PR
• I have updated the docs files (by running dbt docs generate/serve and copying the necessary files into the docs folder)
• I have commented my code as necessary
• I have added at least one Github label to this PR
• My code follows style guidelines
• (Optional) I have recorded a Loom to explain this PR

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