Ensure `eth_GasPrice` API returns proper value

[AnnaShaleva]

Ref. #6 (comment). We need to ensure that eth_GasPrice calculations work as expected wrt the new burning scheme (#163) and Policy's minGasFeeCap related logic introduced in #6.

[AnnaShaleva]

@songb2, cold you please ensure that this API works properly with #230 and #166 and with Metamask? See the original concern is described in #6 (comment).