Creates and/or updates multiple rows in an audience in a single bulk operation. Each entry in the request body includes cell values keyed by columnId. Including a rowId updates that existing row; omitting rowId creates a new row. Both creates and updates can be combined freely in the same request. By default, runEnrichment is false — enrichment does not run automatically; set it to true to trigger enrichment on affected rows after the upsert. To limit enrichment to specific columns, provide columnId values in the columns query parameter; if omitted, all enrichable columns are processed. Returns 200 with data[] row resources — each entry includes id, type, and attributes.values with full cell details (columnId, value, state, and errorDetails when applicable). Returns 400 if the request body is malformed or columnId references are invalid.