minimum gas price should be read out of TxPermission Contract.

[SurfingNerd]

tx permission contract defined a public field: minimumGasPrice.

currently the rpc reports a minimum gas price of 0.

curl -X POST --data '{"jsonrpc":"2.0","method":"eth_gasPrice","params":[],"id":1}' -H "Content-Type: application/json" http://localhost:8540

It's also the case that the RPC accepts transactions with a zero gas price,
even though the mining section of node.toml defined a larger number

min_gas_price = 1000000000

we should get rid of this config entry anyway - because the contract is the source of truth.

No other gas price related setting could be found in the configuring open ethereum section: https://openethereum.github.io/Configuring-OpenEthereum

Code:

fn set_minimal_gas_price(&self, new_price: U256) -> Result<bool, &str> {