DP charges are part of Demat Account related charges and hence doesn’t make a lot of sense to add them in the get_trade_history API. The primary purpose of Trade History API is to serve all historical trade data. Besides this, DP charges are applicable only to sell side and it is a constant value, so you can keep the calculation on your side as well.
You can fetch all charges for your account using Ledger Report API, but that will not be trade wise.