feat: add rpc v2 types and api

[koushiro]

• add rpc v2 types
• add rpc v2 api

[boundless-forest]

I compared some key structs with Geth, The PR is only about the v2 api methods and types, LGTM. However, I am a bit worried about whether the v2 api implementation next will introduce some uncompatibility with the v1 version. It may require the client node resync the db or there is a migration solution.

[koushiro]

However, I am a bit worried about whether the v2 api implementation next will introduce some uncompatibility with the v1 version. It may require the client node resync the db or there is a migration solution.

RPC API is a standalone layer, the compatibility issues like node resync and db migration that you consider should be limited to the implementation of db and mapping-sync level.

Personally, I prefer to provide a mapping abstraction layer under the RPC API layer to manage the mapping of substrate data and ethereum data.