override of pricing portal engine

Summary:

I'm using a Pricing Matrix Template to dynamically calculate the price of a CPQ Part.

The Pricing Matrix Template is configured as follows.

1 input boolean custom pricing attribute 'Input 1' (mapped to a configuration attribute)

3 output pricing attributes:

1. the standard 'Unit Price'
2. a custom charge pricing attribute 'Discount Type OUT'
3. a custom charge pricing attribute 'Discount Value OUT'

Discount Type OUT and the Discount Value OUT are mapped to both the line and the charge Discount Types and Values

When defining the custom output attribute Discount Type OUT and Discount Value OUT, the 'Negotiable' was disabled and there was no way to mark the attributes as Negotiable.