Posthog: stop double reporting UTD events when app is relaunched

[richvdh]

Per element-hq/element-meta#2333

[richvdh]

This follows up on code added in #3206. I think we want to add logic to matrix-sdk-ui::unable_to_decrypt_hook::UtdHookManager to filter out UTD errors that have already been reported the "parent" UTD hook; and we need to persist that data. As with element-hq/element-web#27421, we probably want to use a Bloom filter to avoid the data getting too huge.

It's not quite the same as known_utds, because that is updated when we first see a UTD for a given event. At that point, the report has not yet been sent. If the application is restarted before the max_delay elapses, the task to actually send the report will be killed. In short, we shouldn't update the list of reported UTDs until the report is actually sent.

The main difficulty, I think, is going to be actually connecting UtdHookManager up to some persistent storage.