s3: rename glacier storage class to flexible retrieval

backend/s3/s3.go

@@ -2056,7 +2056,7 @@ If you leave it blank, this is calculated automatically from the sse_customer_ke
 				Help:  "One Zone Infrequent Access storage class",
 			}, {
 				Value: "GLACIER",
-				Help:  "Glacier storage class",
+				Help:  "Glacier Flexible Retrieval storage class",
 			}, {
 				Value: "DEEP_ARCHIVE",
 				Help:  "Glacier Deep Archive storage class",

docs/content/s3.md

@@ -244,7 +244,7 @@ Choose a number from below, or type in your own value
    \ "STANDARD_IA"
  5 / One Zone Infrequent Access storage class
    \ "ONEZONE_IA"
- 6 / Glacier storage class
+ 6 / Glacier Flexible Retrieval storage class
    \ "GLACIER"
  7 / Glacier Deep Archive storage class
    \ "DEEP_ARCHIVE"