allow PurchaseItem from server api OR allow GetStoreItems from server api OR add parameter to client.PurchaseItem to copy customdata

There's actually multiple walls here with multiple solutions... allowing PurchaseItem from the server api is just one of them.

core problem:

- I need store item customdata to be copied over to the inventory item customdata on grant

solutions:

- call a client.PurchaseItem that has a new parameter to copy over the customdata for me

- call a cloudscript that calls a new server.PurchaseItem and then copies over the customdata

- call a cloudscript that calls a new server.GetStoreItems and does all the purchase item stuff manually and copies over the customdata

the best hack I can figure out in the meantime:

- call a cloudscript that uses an http.request to call the client.PurchaseItem api followed by copying over the customdata