[#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/root.go

@@ -0,0 +1,34 @@
+package tree
+
+import (
+	"github.com/spf13/cobra"
+)
+
+var Cmd = &cobra.Command{
+	Use:   "tree",
+	Short: "Operations with the Tree service",
+}
+
+func init() {
+	Cmd.AddCommand(addCmd)
+
+	initAddCmd()
+}
+
+const (
+	containerIDFlagKey = "cid"
+	treeIDFlagKey      = "tid"
+	parentIDFlagKey    = "pid"
+
+	metaFlagKey = "meta"
+)
+
+func initCTID(cmd *cobra.Command) {
+	ff := cmd.Flags()
+
+	ff.String(containerIDFlagKey, "", "Container ID")
+	_ = cmd.MarkFlagRequired(containerIDFlagKey)
+
+	ff.String(treeIDFlagKey, "", "Tree ID")
+	_ = cmd.MarkFlagRequired(treeIDFlagKey)
+}