code: public static Schema decorateRecordSchema(Schema inputSchema, @Nonnull List<Field> fieldList) {
      Preconditions.checkState(inputSchema.getType().equals(Type.RECORD));
      List<Field> outputFields = deepCopySchemaFields(inputSchema);
      List<Field> newOutputFields = Stream.concat(outputFields.stream(), fieldList.stream()).collect(Collectors.toList());
  
      Schema outputSchema = Schema.createRecord(inputSchema.getName(), inputSchema.getDoc(),
              inputSchema.getNamespace(), inputSchema.isError());
      outputSchema.setFields(newOutputFields);
      copyProperties(inputSchema, outputSchema);
      return outputSchema;
    }
docs: Decorate the {@link Schema} for a record with additional {@link Field}s.
  @param inputSchema: must be a {@link Record} schema.
  @return the decorated Schema. Fields are appended to the inputSchema.