Feat: add 'params' to every relaychain RPC requests

[bLd75]

Issue

The relay-chain-rpc-url option works fine with any type of relay chain RPC but is not accepted by smoldot to sync with a light client.
[json-rpc-polkadot] Refused malformed JSON-RPC request: missing field params at line 1 column 59

This is because the params field is not sent by client when no param is required (like here on the initial subscribeNewHeads request).
{"jsonrpc":"2.0","id":0,"method":"chain_subscribeNewHeads"}

Adding an empty params field would allow syncing the relay to a light client.
"params":{}

Steps to reproduce

• clone the smoldot repo / have rust & npm installed
• start the light client/Websocket app: cd bin/wasm-node/javascript then npm install; npm start
• start a para node: polkadot-parachain --chain statemine --relay-chain-rpc-url ws://127.0.0.1:9944/polkadot

[bkchr]

CC @skunert

[skunert]

Fixed by smol-dot/smoldot#13