Report runtime failures

[dominique-pfister]

The current filter pattern [timestamp=*Z, request_id="*-*", event] used by this subscription filter excludes messages that indicate an unexpected exit in the service, e.g.:

RequestId: 66ce6204-7c13-50f6-a32c-3db39caefc6b Error: Runtime exited with error: signal: killed Runtime.ExitError

In order to support this, we should allow setting "" as the filter pattern. We then get all log messages and need to make the standard filter pattern work as well.