[#263] Implement client for exchanging raw messages using gRPC protocol

Implement gRPC client that can uniformly execute any RPC on the remote
server. In the primary implementation, the client is a thin wrapper over
gRPC client connection that is required to create the client. In the future,
it is planned to expand the library with convenient functionality.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

rpc/grpc/util.go

@@ -0,0 +1,13 @@
+package grpc
+
+import (
+	"fmt"
+
+	"github.com/nspcc-dev/neofs-api-go/rpc/common"
+)
+
+const methodNameFmt = "%s/%s"
+
+func toMethodName(p common.CallMethodInfo) string {
+	return fmt.Sprintf(methodNameFmt, p.Service, p.Name)
+}