[#1332] cli: Implement tree add command

It is `TreeService.Add` method implementation.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

cmd/neofs-cli/modules/tree/client.go

@@ -0,0 +1,40 @@
+package tree
+
+import (
+	"context"
+	"strings"
+	"time"
+
+	"github.com/nspcc-dev/neofs-node/cmd/neofs-cli/internal/commonflags"
+	"github.com/nspcc-dev/neofs-node/pkg/network"
+	"github.com/nspcc-dev/neofs-node/pkg/services/tree"
+	"github.com/spf13/viper"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+)
+
+// _client returns grpc Tree service client. Should be removed
+// after making Tree API public.
+func _client(ctx context.Context) (tree.TreeServiceClient, error) {
+	var netAddr network.Address
+	err := netAddr.FromString(viper.GetString(commonflags.RPC))
+	if err != nil {
+		return nil, err
+	}
+
+	opts := make([]grpc.DialOption, 1, 2)
+	opts[0] = grpc.WithBlock()
+
+	if !strings.HasPrefix(netAddr.URIAddr(), "grpcs:") {
+		opts = append(opts, grpc.WithTransportCredentials(insecure.NewCredentials()))
+	}
+
+	// a default connection establishing timeout
+	const defaultClientConnectTimeout = time.Second * 2
+
+	ctx, cancel := context.WithTimeout(ctx, defaultClientConnectTimeout)
+	cc, err := grpc.DialContext(ctx, netAddr.URIAddr(), opts...)
+	cancel()
+
+	return tree.NewTreeServiceClient(cc), err
+}