Removed legacy app launch metric (#37667)

Added time to initial display and time to full display metrics

Author: arti-arutiunov

content/en/real_user_monitoring/rum_without_limits/metrics.md

@@ -29,7 +29,8 @@ Datadog provides the below out-of-the-box metrics for a comprehensive overview o
 
 | Metric Name | Description | Dimensions | Platform |
 |-------------|-------------|------------|----------|
-| `rum.measure.app.startup_time` | App startup time | Default, Percentiles breakdown | Mobile only |
+| `rum.measure.app.startup_to_full_display` | Time to full display during application launch | Default, Percentiles breakdown | Mobile only |
+| `rum.measure.app.startup_to_initial_display` | Time to initial display during application launch | Default, Percentiles breakdown | Mobile only |
 | `rum.measure.error` | Count of errors | Default, Is Crash, View Name | Mobile & Browser |
 | `rum.measure.error.anr` | Count of ANRs (an Android freeze) | Default, Is Crash, View Name | Mobile only |
 | `rum.measure.error.hang` | Count of hangs (an iOS freeze) | Default | Mobile only |
@@ -84,4 +85,4 @@ Metrics can be managed through [APIs][3] or Datadog's dedicated [Terraform modul
 [1]: https://app.datadoghq.com/rum/performance-monitoring
 [2]: /real_user_monitoring/platform/generate_metrics/
 [3]: /api/latest/rum-metrics/
-[4]: https://registry.terraform.io/providers/DataDog/datadog/3.60.0/docs/resources/rum_metric
+[4]: https://registry.terraform.io/providers/DataDog/datadog/3.60.0/docs/resources/rum_metric