probe: address the impact of sanctions on crash reporting

This issue is about addressing the impact of sanctions on crash reporting. Like we documented for geolocation services in https://github.com/ooni/probe/issues/1988, there's an impact on sanctions also on Sentry. We'll consider this issue resolved when we've decided whether and how to address this mobile(-only?) issue.

The logcat of a device in a country under sanctions (i.e., Cuba, Syria, Iran, North Korea) looks like the following:

[...] I/Sentry: Not possible to read external files directory

Luckily, the test lists already contain some Sentry domains, so, e.g., we see that Sentry returns 403 to users in Iran. We say this is server-side blocking because the test helper gets a 404 response instead. (This measurement falls under the chapter of measuring server-side blocking, which is one of the topics on which we are working recently.)

I am not sure what a reasonable next step could look like here. Given infinite team capacity, I would probably investigate whether we could have a self-hosted sentry service. Yet, I am not sure we have infinite team capacity. Then, it may perhaps make sense to try to gauge what the missing crash reports could be based on the existing crash reports. Yet, this exercise seems dangerously close to estimating how are airplanes are hit and downed during a dogfight by looking at the damage in airplanes that survived a battle. Therefore, I think I'm just going to put this issue into the agenda of the next frontend meeting so that we can have a full team discussion.