[In App Messaging] Doc clarification reg scheduling campaigns based on delayed events

## What feature would you like to see?

Please clarify campaign compose [documentation](https://firebase.google.com/docs/in-app-messaging/compose-campaign#schedule-your-message) regarding trigger events and the impact of [delayed firebase analytics events](https://firebase.google.com/docs/analytics/debugview?authuser=0).

**Campaign Compose docs**

**Firebase Analytics Events docs**

## How would you use it?

I would like to understand how reliable In app messaging can be when analytics events are batched and sent after a while. It is possible that users aren't engaged with the app anymore.

Start with the linked In-App Messaging Campaign Compose section, especially “Schedule your message,” and compare it with the linked Firebase Analytics DebugView documentation. Clarify how delayed or batched Analytics trigger events affect campaign scheduling and whether users must still be engaged when events arrive; done means the documentation answers the reliability concern directly.

Written by the indexing model from the issue text.