Investigate: new JSON-RPC

[Niederb]

Parity is working on a new JSON-RPC API. We should look into this and figure out if/how we want to support it.

• Old API: https://polkadot.js.org/docs/substrate/rpc/#author
• New API: https://paritytech.github.io/json-rpc-interface-spec/introduction.html

Questions:

• Are there concrete plans to deprecate the old API?
• Is there a replacement to all calls we need?

Some links/references:

• https://forum.polkadot.network/t/new-json-rpc-api-mega-q-a/3048
• https://github.com/paritytech/json-rpc-interface-spec/pull/147
• https://forum.polkadot.network/t/polkadot-api-2023-q4-update/5318