Fix/4561

[dsilhavy]

This PR addresses #4561.

• Adds a new setting deleteEventMessageDataAfterEventStarted set to true by default. If this flag is enabled, the EventController will delete the messageData and the parsedMessageData of events after they have been started. This is to save memory in case events have a long duration and need to be persisted in the EventController for a while to not be retriggered.
• Note: Applications will receive a copy of the original event data when they subscribe to an event. This copy contains the original message data and is not affected by deleteEventMessageDataAfterEventStarted. Only if an event is dispatched for the second time (e.g. when the user seeks back) the message data will not be included in the dispatched event. In this case, the app would need to persist the messageData if required.

I am open for feedback on this one. As an alternative, we could also define an eventMessagePersistDuration after which we delete the payload.

In any case, we need to find a solution for events that have a long duration, as outlined in #4561.