Fix issue of always send x-ms-encryption-algorithm header in request. (Azure#20732)

Author: EmmaZhu

sdk/storage/storage-blob/src/generated/src/models/parameters.ts

@@ -1332,4 +1332,14 @@ directive:
       $["HasVersionsOnly"]["description"] = "Inactive root blobs which have any versions would have such tag with value true.";
 ```
 
+### Use string union instead of string for EncryptionAlgorithm
+
+```yaml
+directive:
+  - from: swagger-document
+    where: $.parameters.EncryptionAlgorithm
+    transform: >
+      $["x-ms-enum"]["modelAsString"] = true;
+```
+
 ![Impressions](https://azure-sdk-impressions.azurewebsites.net/api/impressions/azure-sdk-for-js%2Fsdk%2Fstorage%2Fstorage-blob%2Fswagger%2FREADME.png)