ADD: added basic backend function plus a mockup for a cli interface

backend/cmd/cli/user/user.go

@@ -0,0 +1,13 @@
+package user
+
+import "github.com/spf13/cobra"
+
+var UserCmd = &cobra.Command{
+	Use:   "user",
+	Short: "User management",
+}
+
+func init() {
+	UserCmd.AddCommand(listCmd)
+	UserCmd.AddCommand(getCmd)
+}