Support `crashed` session events in Ruby SDK

[Fwang36]

Currently, we are not sending the crashed session event type in the Ruby SDK. This leads to users of the Ruby SDK and the Release Health feature to always have 100% Crash Free Rate, even if the errors themselves are marked as unhandled.

We should support sending crashed session events for unhandled errors so Release Health works properly

[sandstrom]

Don't know if this is the right place, but would be great if the Ruby SDK supported the release health stuff.

https://docs.sentry.io/product/releases/setup/

According to this doc page it's not yet supported in the Ruby SDK.