Find grpc

[emadolsky]

This PR introduces find gRPC alongside unary interceptors which share a lot of logic from already implemented stream interceptors. Some minor refactors have been applied in order to reduce code copy.

Notes:

• The same cache logic as the HTTP implementation is used for gRPC. However, because of the data compatibility, and to avoid unnecessary Marshal/Unmarshal the cache space for grpc-find and regular find are separated.
• getWithCache function is implemented to simplify the caching code and to avoid partial fixes happened before because of the code duplication in the future.
• There are still bunch of duplicated codes around the ratelimiter handlers (middleware, interceptor), but I let them be for now. If the reviewers believe it's better to refactor those parts as well, I'll spend some time on it.