[Feature request] generate gRPC query clients from protobuf

[larry0x]

I want to write native Rust code to query an Osmosis node via gRPC. However, whereas osmosis-std comes with cosmwasm queriers, it doesn't come with gRPC query clients. I had to create my own version of proto-build (forked from cosmos-rust repo) and generate my own Osmosis Rust code: https://github.com/larry0x/osmosis-proto

It'd be great if osmosis-std also comes with gRPC query clients. It can be put behind an optional "grpc" feature, so when used in contracts, developers only need to turn off this feature (since grpc stuff isn't wasm-compatible). Happy to do a PR on this