Skip user agent HTTP header validation (microsoft#10279)

* Skip user agent HTTP header validation

In microsoft#8392, we added logic to skip HTTP header validation for
`User-Agent` in the NetworkingModule. Now that NetworkingModule is being
refactored, we need this change in the new implementation.

This change skips user agent validation in the new networking module.

* Change files

Author: JunielKatarn

vnext/Shared/Networking/WinRTHttpResource.cpp

@@ -229,6 +229,13 @@ namespace Microsoft::React::Networking {
           co_return m_onError(coReqArgs->RequestId, "Failed to append Authorization");
         }
       }
+      else if (boost::iequals(header.first.c_str(), "User-Agent")) {
+        bool success =
+          coRequest.Headers().TryAppendWithoutValidation(to_hstring(header.first), to_hstring(header.second));
+        if (!success && m_onError) {
+          co_return m_onError(coReqArgs->RequestId, "Failed to append User-Agent");
+        }
+      }
       else {
         try {
           coRequest.Headers().Append(to_hstring(header.first), to_hstring(header.second));