Import a complete marketplace configuration from a JSON file previously exported.
  This endpoint accepts the exported JSON file as a multipart/form-data upload.
  
  **Import Process:**
  - Uploads and validates the JSON file structure
  - Generates new IDs for all entities to avoid conflicts
  - Maps connection relationships in requests and sessions
  - Assigns to the specified tenant and cobrand
  - Creates audit trail entries for all imported items
  - Handles cross-environment imports with brand code mapping
  
  **Important Notes:**
  - This creates new marketplace entities; it does not update existing ones
  - Connection names are used to maintain relationships during import
  - Sensitive data like client secrets are regenerated for security
  - Import supports cross-environment scenarios with brand code mapping
.