Kusama and Polkadot does not support RPC http anymore

[dakk]

The default method for api is now websocket from this endpoint: ws://127.0.0.1:9944, so we need to migrate all the RPC calls to SubstrateInterface, and bind SubstrateInterface to the websocket endpoint.

Other substrate interfaces may continue using rpc, so we can first implement these modification by extending substrate for Polkadot and Kusama. Anyway the modification is applied to the substrate codebase:
paritytech/substrate#13384