Bitswap protocol support & RPC endpoints

[dmitry-markin]

For retrieving data from bulletin chain nodes using smoldot we need to support Bitswap protocol. Server-side support of Bitswap is already implemented in substrate, so we just need to implement client support on smoldot side. Additionally, we need to expose two RPC methods for data fetching via Bitswap:

1. bitswap_v1_get(cid) for synchronous download of a single CID.
2. bitswap_v1_stream(cids) for requesting multiple CIDs. Chunks are returned (streamed) as they are downloaded from the peers.

The RPC endpoints will be defined in https://github.com/paritytech/json-rpc-interface-spec/.