Make default container name lowercase as capital letters are not allowed

Author: fkuehnSAG

src/Samhammer.AzureBlobStorage/Client/DefaultAzureBlobStorageClientFactory.cs

@@ -20,7 +20,7 @@ public BlobServiceClient GetClient(BlobClientOptions options = null)
 
         public string GetDefaultContainerName()
         {
-            return Options.Value.ContainerName;
+            return Options.Value.ContainerName.ToLower();
         }
     }