Add Missouri CSFP county filtering

[daphnehanse11]

Missouri CSFP should be county-filtered for launch, similar to the Kansas and Massachusetts handling. The Missouri DHSS CSFP page links a CSFP Site Map for distribution sites, and the state plan says people served by the program must reside in the service area of the local agency where they apply.

Implementation notes:

• Add a Missouri-specific CSFP county eligibility variable based on the DHSS CSFP site layer.
• Gate federal commodity_supplemental_food_program_eligible by this variable when state_code is MO.
• Include tests for a covered county, St. Louis city, and a Missouri county absent from the site layer.

Sources:

• https://health.mo.gov/living/wellness/nutrition/foodprograms/csfp/
• https://health.mo.gov/living/wellness/nutrition/foodprograms/csfp/pdf/missouri-state-plan-ada.pdf
• https://www.arcgis.com/home/item.html?id=d8d8553132194b2ebd038d171503e16c
• https://gis.mo.gov/arcgis/rest/services/DHSS/commodityFood/MapServer/0