BTCGateway: bind Exocore address from Bitcoin by op_return

[adu-web3]

Description

When users deposits, they will simultaneously bind the deposit bitcoin address with an exocore address by specifying it in the op_return output. But we need to decide whether the users need to specify this binding address in op_return output for each deposit tx

[bwhour]

Currently, we assume it binds according to the one-to-one and unchanging principle. but we can change it if customer need one-to-more while deposit.