add_product method does not accpet location_id

[MCHellspawn]

The add_product method of the grocy class doesn't allow for setting the location id. It looks like it's undocumented but the /stock/products/{productId}/add API method does take it:
{
"amount": 1,
"best_before_date": "2023-01-19",
"transaction_type": "purchase",
"location_id": 6
}

This does work in the API. It would be useful if this could be added to the add_product method in the class.

I have actually already completed the changes in a fork and I am ready to submit a pull request if you would accept it.