Merge pull request 'chore: update discount type for get calculation for buy assets' (#18) from chore-update-buy-calc-discount into v2

Reviewed-on: #18

wallet/v1/msg.proto

@@ -561,7 +561,7 @@ message CalcBuyAssetRes {
   BuyAssetSide side = 1;
   int64 calculated_irt_amount = 2;
   double calculated_asset_amount = 3;
-  int64 discount_amount = 4;
+  AssetDiscountRes discount_amount = 4;
   Commission commission = 5;
   // double buy_min_amount = 7;
 }