fix: exclude 4xx client errors from Application Insights failures (#2865)

* fix: exclude 4xx client errors from Application Insights failures

Add TelemetryProcessor to mark 4xx responses as success=true.
Only 5xx server errors should appear in the Failures dashboard.

This reduces noise from expected client errors (400 Bad Request,
401 Unauthorized, 404 Not Found) in failure metrics and alerts.

* fix: use correct type for responseCode (string, not number)

Application Insights SDK types define responseCode as string.
Use parseInt() for proper type conversion before comparison.

Author: TaprootFreak

src/main.ts

@@ -26,6 +26,19 @@ async function bootstrap() {
   if (process.env.APPINSIGHTS_INSTRUMENTATIONKEY) {
     AppInsights.setup().setAutoDependencyCorrelation(true).setAutoCollectConsole(true, true);
     AppInsights.defaultClient.context.tags[AppInsights.defaultClient.context.keys.cloudRole] = 'dfx-api';
+
+    // Don't mark 4xx client errors as failures - only 5xx are real server errors
+    AppInsights.defaultClient.addTelemetryProcessor((envelope) => {
+      const data = envelope.data as { baseType?: string; baseData?: { responseCode?: string; success?: boolean } };
+      if (data.baseType === 'RequestData' && data.baseData?.responseCode) {
+        const responseCode = parseInt(data.baseData.responseCode, 10);
+        if (responseCode >= 400 && responseCode < 500) {
+          data.baseData.success = true;
+        }
+      }
+      return true;
+    });
+
     AppInsights.start();
   }