[docs] Add troubleshooting use cases around crash analytics

There could be different reasons why crash events don't reach ES or aren't easily visible there, such as trying them while having Xcode's debugger attached or not relaunching the app after the crash (the next launch is where the crash is actually exported). Right now, we don't mention these anywhere, which can make the testing experience frustrating, so we should mention these in our troubleshooting docs.