operations: implement --partial-suffix to control extension of temporary file names

docs/content/docs.md

@@ -1278,8 +1278,9 @@ flag set) such as:
 - sftp
 
 Without `--inplace` (the default) rclone will first upload to a
-temporary file with an extension like this where `XXXXXX` represents a
-random string.
+temporary file with an extension like this, where `XXXXXX` represents a
+random string and `.partial` is [--partial-suffix](#partial-suffix) value
+(`.partial` by default).
 
     original-file-name.XXXXXX.partial
 
@@ -1726,6 +1727,15 @@ If you want perfect ordering then you will need to specify
 [--check-first](#check-first) which will find all the files which need
 transferring first before transferring any.
 
+### --partial-suffix {#partial-suffix}
+
+When [--inplace](#inplace) is not used, it causes rclone to use
+the `--partial-suffix` as suffix for temporary files.
+
+Suffix length limit is 16 characters.
+
+The default is `.partial`.
+
 ### --password-command SpaceSepList ###
 
 This flag supplies a program which should supply the config password