Enable eth_gasPrice

[yarkinwho]

We disabled this API as it will not return correct values during the process of gas fee changes.

But now
1 the gnosis-safe project require this in some batch requests.
2 It can only be visited via batch requests. (Regular calls will be routed to Miner in our system)
3 The cases when this API not working properly is really rare and we have full control to it (e.g. the timing to apply the price changes).

Therefore, it should be fine to expose this API.