s3: Add INTELLIGENT_TIERING storage class

For Intelligent-Tiering:
https://aws.amazon.com/s3/storage-classes/#Unknown_or_changing_access

backend/s3/s3.go

@@ -653,6 +653,9 @@ isn't set then "acl" is used instead.`,
 			}, {
 				Value: "DEEP_ARCHIVE",
 				Help:  "Glacier Deep Archive storage class",
+			}, {
+				Value: "INTELLIGENT_TIERING",
+				Help:  "Intelligent-Tiering storage class",
 			}},
 		}, {
 			// Mapping from here: https://www.alibabacloud.com/help/doc-detail/64919.htm

docs/content/s3.md

@@ -222,6 +222,8 @@ Choose a number from below, or type in your own value
    \ "GLACIER"
  7 / Glacier Deep Archive storage class
    \ "DEEP_ARCHIVE"
+ 8 / Intelligent-Tiering storage class
+   \ "INTELLIGENT_TIERING"
 storage_class> 1
 Remote config
 --------------------
@@ -930,6 +932,8 @@ The storage class to use when storing new objects in S3.
         - Glacier storage class
     - "DEEP_ARCHIVE"
         - Glacier Deep Archive storage class
+    - "INTELLIGENT_TIERING"
+        - Intelligent-Tiering storage class
 
 #### --s3-storage-class