backend: add Linkbox backend

Add backend for linkbox.io with read and write capabilities

fixes #6960 #6629

docs/content/linkbox.md

@@ -0,0 +1,76 @@
+---
+title: "Linkbox"
+description: "Rclone docs for Linkbox"
+versionIntroduced: "v1.65"
+---
+
+# {{< icon "fa fa-infinity" >}} Linkbox
+
+Linkbox is [a private cloud drive](https://linkbox.to/).
+
+## Configuration
+
+Here is an example of making a remote for Linkbox.
+
+First run:
+
+     rclone config
+
+This will guide you through an interactive setup process:
+
+```
+No remotes found, make a new one?
+n) New remote
+s) Set configuration password
+q) Quit config
+n/s/q> n
+
+Enter name for new remote.
+name> remote
+
+Option Storage.
+Type of storage to configure.
+Choose a number from below, or type in your own value.
+XX / Linkbox
+   \ (linkbox)
+Storage> XX
+
+Option token.
+Token from https://www.linkbox.to/admin/account
+Enter a value.
+token> testFromCLToken
+
+Configuration complete.
+Options:
+- type: linkbox
+- token: XXXXXXXXXXX
+Keep this "linkbox" remote?
+y) Yes this is OK (default)
+e) Edit this remote
+d) Delete this remote
+y/e/d> y
+
+```
+
+{{< rem autogenerated options start" - DO NOT EDIT - instead edit fs.RegInfo in backend/linkbox/linkbox.go then run make backenddocs" >}}
+### Standard options
+
+Here are the Standard options specific to linkbox (Linkbox).
+
+#### --linkbox-token
+
+Token from https://www.linkbox.to/admin/account
+
+Properties:
+
+- Config:      token
+- Env Var:     RCLONE_LINKBOX_TOKEN
+- Type:        string
+- Required:    true
+
+{{< rem autogenerated options stop >}}
+
+## Limitations
+
+Invalid UTF-8 bytes will also be [replaced](https://rclone.org/overview/#invalid-utf8),
+as they can't be used in JSON strings.