Update effective dates for facility-group association

Updates the effective start date and/or termination date for a facility-group association. Use this to adjust when a facility's membership in a group begins or ends; use PUT .../groups/{certifyGroupId}/networks/{networkId}/effective-date to independently adjust a single network enrollment date within that group association instead. Optionally cascades the date change to network participation based on the cascadeToNetworkParticipation flag — this cascade is best-effort: if it fails, the failure is swallowed and does not fail the request or change the response, so a 200 does not guarantee the cascade itself succeeded. If terminationDate is provided, it must be after the effectiveDate. Mirrors the practitioner-group precedent endpoint with one deliberate divergence: the request body carries an optional changeReason field per facility-resource convention. Returns the raw updated TenantGroupFacility record as an untyped JSON object, not a curated response DTO.