[FEATURE] Turn on gRPC server reflection

[alexeykiselev]

Аbstract
To simplify the usage of node's gRPC API enable built-in gRPC reflection server following the instructions.

Motivation and Purposes
For now, the node's gRPC API could be discovered only by downloading and embedding Protobuf schemes in a client application.

Examples and implementations
The examples are available at known implementations page.