State Proofs: Return proofs in gRPC/REST

[ashcherbakov]

Cosmos-sdk doesn't return any state proofs in gRPC/REST queries, see cosmos/cosmos-sdk#7036.
As REST is supposed to be one of the main ways for communication with nodes, we need to return them.

Options:
O1: Contribute to cosmos-sdk (probably requires communication and check of the design with cosmos maintainers)
O2: Explicitly return state proofs as one of the values in every DCL query response

• just add this parameter to query.proto for every response and every module
• generate the response appropriately.
• An example where a similar approach is used: link and link

Please note, that

• This change doesn't make much sense if clients don't verify the proofs on their side (see State Proofs: Verify proofs in gRPC/REST on platforms and languages supported by Tendermint/Cosmos #186 or State Proofs: Client SDK for communication with nodes - Design #187)
• We may decide not to support proofs in gRPC/REST (and hence don't work on this task) if we create a client SDK based on Tendermint RPC which has state proofs out of the box (see State Proofs: Client SDK for communication with nodes - Design #187).
• Only single value queries (that is quering items stored in Store directly) will be supported. For example get-model will have a state proof returned, while get-all-models will not.
  Multi value proofs support is a separate task: State Proofs: Light client for lists #34.