docs: make the JSON-RPC page its own section

Make JSON-RPC page it's own section similar to Mirror Node, also all the API details similar to MN for easy reference. Inspiration for layouts can be taken for similar products in the EVM ecosystem such as [Alchemy](https://docs.alchemy.com/reference/ethereum-api-endpoints), [Infura](https://docs.infura.io/api/networks/ethereum/json-rpc-methods) etc

follow up to issue #810 