Support for combo HTTP server

[andri lim]

In nimbus-eth1, we provide services such as json-rpc, graphql, ws-rpc, engine-api, and ws-engine-api.
Each have their own http server. It also means nimbus-eth1 also using lot of different ports for these services.
It would be good if we can combine them like other clients. We can group json-rpc, graphql, and ws-rpc into one server.
And the other server will serve engine-api and ws-engine-api. So instead of using 5 different servers/ports, we only use 2 servers/ports.