✨ Create test model for KF study

[awarkow]

Create model for KF test study (SD_1NNS3K8V)

This PR creates example models for a KF study, using source data from the existing Kids First Dataservice. To build the model, users will need to download source files from DS to load as seed files before running dbt.

Please reach out to @awarkow or @Christina-J-Diaz for these seed files.

Continues ongoing work under DFF Epic D3B-2115

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality
  to not work as expected)
• This change requires a documentation update

TODO: Implement tests and run through checklist

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide
instructions so we can reproduce. Please also list any relevant details for
your test configuration

• Test A
• Test B

Test Configuration:

• Environment:
• Test files:

Checklist

Please check all of the items below before merging this pull request. If an
item in the list below does not need to be completed, please indicate the
reason why.

• I ensured that all tables have proper source and ref definitions
• I Defined {{ config(schema=[schema name], tags = [list, of, tags]) }} at
  the start of each script
• I have performed a self-review of my own code
• I have checked my code and corrected any misspellings
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature
  works
• My code follows the style guidelines of this project
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes
• I have committed any related changes to the PR
• Run sqlfluff fix on tables that are created or modified in this PR.

[awarkow]

agreed that this would be useful to populate