add example for FlushWithContext() (#12308)

Author: ribice

platform-includes/configuration/drain-example/go.mdx

@@ -16,3 +16,17 @@ func main() {
 	sentry.CaptureMessage("my message")
 }
 ```
+
+`FlushWithContext` is an alternative to Flush that uses a context.Context to manage the timeout or cancellation of the flush operation. This approach is particularly useful in applications where you are already using contexts for managing deadlines and cancellations.
+
+
+```go
+func main() {
+	// err := sentry.Init(...)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	sentry.CaptureMessage("my message")
+	sentry.FlushWithContext(ctx)
+}
+```