Requesting state does not have the request body described

[EclesioMeloJunior]

Description

Inside the spec in the section 4.8.4. Requesting States the definition 44 for State Request does not define all the available fields to execute the request, neither explains the the request is a Protobuf serialized structure, while the definition 42 for Block Request defines the request fields and also explains the request format.

The current format can be found at https://github.com/paritytech/substrate/blob/master/client/network/sync/src/schema/api.v1.proto and would be fine to have it define in the spec under definition 44