Adds one or more columns to an existing audience in a single bulk operation. Columns define the data fields available for each row in the audience; each column has a name, a dataType (e.g., TEXT, INTEGER, EMAIL, DATE, BOOLEAN), and behavior flags (isFrozen, isHidden). CUSTOM (dataSource: CUSTOM) columns hold static user-provided values. ZOOMINFO_MATCH (dataSource: ZOOMINFO_MATCH) columns are enrichment-driven and require matchCriteria referencing existing columnId values in the audience — create those source columns first before adding match columns. Returns 201 Created with the full array of created column resources including system-assigned columnId values and read-only flags. Returns 400 if required fields are missing, dataType is invalid, or matchCriteria references a non-existent columnId. Returns 404 if no audience matches the provided audienceId.