Add status date to the application status changes API

Worker assignment write payloads accept optional top-level type

Children API exposes counties on read and write

POST /api/v1/worker_assignments (child case-carrying)

Children API exposes counties on read and write

POST /api/v1/application_status_changes

Applications: link to placement provider; better profile fields when the provider is nested

Placement providers: update endpoint and list filters

POST /api/v1/background_check_logs now requires an application relationship and updates if exists

Added POST /api/v1/applications/:application_id/documents for creating documents (ApplicationMiscFile) via the API.