Enhancing example content for frontend and backend

Author: codyde

docs/platforms/javascript/common/tracing/span-metrics/custom-instrumentation/index.mdx

@@ -1,5 +1,5 @@
 ---
-title: Custom Span Instrumentation
+title: Building Custom Spans
 description: "Learn how to capture performance data on any action in your app."
 sidebar_order: 20
 ---