Add Elastic Cloud watcher for seg faults in staging

If a Ruby seg faults occurs, we should know about it ASAP. This is a corrective action for gitlab-com/gl-infra/production#6276 (closed).

Inspired by !4134 (merged)

Testing

1. Generated JSON via jsonnet elastic/managed-objects/nonprod-log/watches/segfault_crash.jsonnet | pbcopy
2. Created a watcher in https://nonprod-log.gitlab.net/app/management/insightsAndAlerting/watcher/watches.
3. Tweaked the time interval from 17m to 7d and edit the test message.
4. Clicked Simulate and executed it right away.