exporthistory: strip all trailing slashes from blob prefix

Author: bachuv

exporthistory/src/main/java/com/microsoft/durabletask/exporthistory/activities/ExportInstanceHistoryActivity.java

@@ -87,8 +87,14 @@ public Object run(TaskActivityContext ctx) {
 
             // Generate blob name
             String blobFileName = generateBlobFileName(completedTimestamp, instanceId, input.getFormat().getKind());
-            String blobPath = input.getDestination().getPrefix() != null
-                    ? input.getDestination().getPrefix().replaceAll("/$", "") + "/" + blobFileName
+            String prefix = input.getDestination().getPrefix();
+            if (prefix != null) {
+                while (prefix.endsWith("/")) {
+                    prefix = prefix.substring(0, prefix.length() - 1);
+                }
+            }
+            String blobPath = prefix != null
+                    ? prefix + "/" + blobFileName
                     : blobFileName;
 
             // Serialize