Add gas station default gas price

[ggobugi27]

For cross-chain-transfer option, user without a gas paying account is by default set to gas station kadena-xchain-gas.

In addition to the setting the default gas station, we should also set the finishing transaction's gas price to meet the gas station's requirement (1e-8). Currently, chainweaver default gas price to 0.0001 regardless of usage of gas station, and this leads to validation failure of the finishing step.