Add a fee query to GenericMarketMaking bot like BatchExecutor has

[bghughes]

Note that in #26, we add the fee query ONLY TO THE BATCH EXECUTOR so on OP we know what gasPrice to use. This should be extended to the generic class as well and for now, it is not supported and the generic class may cause users to overpay for gas on OP Mainnet until this is in place.

Perhaps an approach that is chain-specific can be good too as this will only pertain to OP AFAIK. cc #25