backend: add Linkbox backend

Add backend for linkbox.io with read and write capabilities

fixes rclone#6960 rclone#6629

Author: Viktor-Yakovchuk

README.md

@@ -53,6 +53,7 @@ Rclone *("rsync for cloud storage")* is a command-line program to sync files and
   * Koofr [:page_facing_up:](https://rclone.org/koofr/)
   * Leviia Object Storage [:page_facing_up:](https://rclone.org/s3/#leviia)
   * Liara Object Storage [:page_facing_up:](https://rclone.org/s3/#liara-object-storage)
+  * Linkbox [:page_facing_up:](https://rclone.org/linkbox)
   * Linode Object Storage [:page_facing_up:](https://rclone.org/s3/#linode)
   * Mail.ru Cloud [:page_facing_up:](https://rclone.org/mailru/)
   * Memset Memstore [:page_facing_up:](https://rclone.org/swift/)

backend/all/all.go

@@ -28,6 +28,7 @@ import (
 	_ "github.com/rclone/rclone/backend/internetarchive"
 	_ "github.com/rclone/rclone/backend/jottacloud"
 	_ "github.com/rclone/rclone/backend/koofr"
+	_ "github.com/rclone/rclone/backend/linkbox"
 	_ "github.com/rclone/rclone/backend/local"
 	_ "github.com/rclone/rclone/backend/mailru"
 	_ "github.com/rclone/rclone/backend/mega"