s3: Support Alibaba Cloud (Aliyun) OSS

The existing s3 backend passed all integration tests with OSS provided
`force_path_style = false`.

This makes sure that is so and adds documentation and configuration
for OSS.

Thanks to @luolibin for their work on the OSS backend which we ended
up not needing.

Fixes #1641
Fixes #1237

README.md

@@ -20,6 +20,7 @@ Rclone *("rsync for cloud storage")* is a command line program to sync files and
 
 ## Storage providers
 
+  * Alibaba Cloud (Aliyun) Object Storage System (OSS) [:page_facing_up:](https://rclone.org/s3/#alibaba-oss)
   * Amazon Drive [:page_facing_up:](https://rclone.org/amazonclouddrive/) ([See note](https://rclone.org/amazonclouddrive/#status))
   * Amazon S3 [:page_facing_up:](https://rclone.org/s3/)
   * Backblaze B2 [:page_facing_up:](https://rclone.org/b2/)