Modify gRPC configuration parameters in Config class

[antas-marcin]

This PR changes how we configure gRPC connection in Java client.

Assuming that REST endpoint works on localhost:8080 and gRPC endpoint works on localhost:50051

1. One can set the gRPC settings using Config constructor:

new Config("https", "localhost:8080", null, 10, false, "localhost:50051")

3. One can set gRPC settings using setGRPCSecured and setGRPCHost methods:

Config config = Config config = new Config("http", "localhost:8080");
config.setGRPCSecured(false);
config.setGRPCHost("localhost:50051");