Add utf8 with bom (#2641)

* Change default file encoding

src/Sdk/DTPipelines/Pipelines/ObjectTemplating/YamlObjectReader.cs

@@ -569,4 +569,4 @@ namespace GitHub.DistributedTask.Pipelines.ObjectTemplating
         private readonly Parser m_parser;
         private ParsingEvent m_current;
     }
-}
+}