Add Oasis Core's client gRPC protocol version to -version flag's output

[tjanez]

Once Oasis Core's client gRPC protocol is versioned (https://github.com/oasisprotocol/oasis-core/issues/1861), include its version in -version flag's output.

It should be included under the Oasis Core group, e.g.:

Software version: 1.0.0
Oasis Core:
  Software version:             20.12.2
  Client gRPC protocol version: 1.0.0
Rosetta API version: 1.4.1
Go toolchain version: 1.15.5