[CNT-144] OSS General Prepare Contract Type Support

The new smart contract architecture has two input addresses in function call transaction, so we need oss to support it.
 
OSS 這支 API 支援 op_return 且 type 為 contract
base/v1/general-transaction/prepare
 
交易範例
TX_ID
```
user_addr  amount(color) -> p2sh_addr1 amount(color)

                            p2sh_addr2 amount(color)

                            op_return amount(color) 
```