Add eth_ operations to the Lotus Gateway

[maciejwitowski]

This is a tracking issue for filecoin-project/ref-fvm#1214

Quoting the original one for completeness:

Hello devs,

Glif nodes provider is here.
Right now we have a doubt how to give users access to the wss endpoint. The main pain is eth_subscribe operation - it is require write permissions.
For now we have 2 models of access to the wss:

1. Lotus Gateway, but it is limited only for Filecoin operations
2. Access with JWT token with read, write permissions - but this isn't weapon of choice - write permissions are too wide.

I believe the easiest way will be to add eth operations to the Lotus Gateway.

The place where the Lotus Gateway code is placed: https://github.com/filecoin-project/lotus/blob/release/fevm-wallaby/api/api_gateway.go