Remove userAgent tag from HttpClient activity (#5110)

Author: vishweshbankwar

src/OpenTelemetry.Instrumentation.Http/CHANGELOG.md

@@ -23,6 +23,9 @@
   `HttpClientTraceInstrumentationOptions`.
   ([#5109](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5109))
 
+* **Breaking Change**: Removed `http.user_agent` tag from HttpClient activity.
+  ([#5110](https://github.com/open-telemetry/opentelemetry-dotnet/pull/5110))
+
 ## 1.6.0-beta.3
 
 Released 2023-Nov-17

src/OpenTelemetry.Instrumentation.Http/Implementation/HttpHandlerDiagnosticListener.cs

@@ -167,15 +167,6 @@ public void OnStartActivity(Activity activity, object payload)
 
             activity.SetTag(SemanticConventions.AttributeUrlFull, HttpTagHelper.GetUriTagValueFromRequestUri(request.RequestUri));
 
-            if (request.Headers.TryGetValues("User-Agent", out var userAgentValues))
-            {
-                var userAgent = userAgentValues.FirstOrDefault();
-                if (!string.IsNullOrEmpty(userAgent))
-                {
-                    activity.SetTag(SemanticConventions.AttributeHttpUserAgent, userAgent);
-                }
-            }
-
             try
             {
                 this.options.EnrichWithHttpRequestMessage?.Invoke(activity, request);