Implement Da Vinci PDex payer-to-payer bulk data exchange to transfer a member's clinical data from a prior payer to a new payer

Verified steps

1. After successfully executing $member-match, obtain the member's prior payer identifier and use it to request the member's data via the prior payer's FHIR Bulk Data endpoint using a Group-level or Patient-level $export.
2. Authenticate using SMART Backend Services (system-level client credentials) with the appropriate system-level scopes required for payer-to-payer access as defined in the PDex IG.
3. Issue a GET request to [base]/Patient/[id]/$export or the appropriate Group export endpoint with _type parameter to request the relevant resource types (ExplanationOfBenefit, Condition, MedicationRequest, Procedure, Observation, etc.).
4. Poll the Content-Location URL returned in the 202 response using the async pattern: check the polling URL until the response is 200 with the output manifest, then download each NDJSON file.
5. Process the downloaded NDJSON files, validating each resource against the applicable PDex and CARIN BB profiles, and ingest the data into the new payer's FHIR store.
6. Document any resources that failed validation or could not be mapped and generate a provenance chain using FHIR Provenance resources to record the data origin from the prior payer.