Be able to specify which thread is the "crashed" one in a minidump envelope

[vthib]

This is very much in line with this discussion: #946

The issue is that the current handling of minidumps does not work well with some watchdog/monitoring implementations, where a thread will detect that another thread is stuck, which works like this:

• A dedicated thread (T) is used for monitoring
• This thread T detects that the thread T2 is unresponsive/faulty/etc, and generates a minidump to send to sentry
• Sentry displays this dump by highlighting the threat T as the "crashed" one, and not T2

This makes complete sense, since the dump generator cannot know which thread caused the issue. However, it makes it very hard to debug those issues because:

• All those dumps are merged into a single same issue
• The faulty thread is not highlighted and must be search by hand through the whole list.

To fix this, we would need a way to specify to sentry which thread to highlight. I originally thought that using Exception > thread_id attribute could work, but the discussion makes it clear that it does not.

Hence this feature request issue. Would it be possible to handle this case, ie if the Exception > thread_id attribute is set, pick this one to higlight instead of the thread marked as "crashed".

Thanks!