Adds missing builderFee in UserFillSchema type

[0xwetzo]

When an order is placed from an external UI, the UI builder may have set a builder fee that is in the UserFillSchema response, between fee and tid.

[nktkas]

Hey @0xwetzo.
Can you provide an example of an address where the API returns the builderFee field?
Coverage tests must be added for this field to prove that it actually exists.

[0xwetzo]

Hey @nktkas,
Sure, here is one: 0xC6fC56A97948F04587730721e8Fd7CB37559378e

[nktkas]

Thanks for your contribution!