Update Data Lake service URL endpoint sample to use HTTPS (Azure#25654)

Author: scottaddie

sdk/storage/azure-storage-file-datalake/src/samples/java/com/azure/storage/file/datalake/AppendFlushExample.java

@@ -41,7 +41,7 @@ public static void main(String[] args) throws IOException {
          * From the Azure portal, get your Storage account dfs service URL endpoint.
          * The URL typically looks like this:
          */
-        String endpoint = String.format(Locale.ROOT, "http://%s.dfs.core.windows.net", accountName);
+        String endpoint = String.format(Locale.ROOT, "https://%s.dfs.core.windows.net", accountName);
 
         /*
          * Create a DataLakeServiceClient object that wraps the service endpoint, credential and a request pipeline.