Ignore end_time when generating automatic payload

This fixes a bug where an alert that does not provide an explicit fingerprint param could not be auto resolved.

end_time was introduced in !41648 (merged).

When a fingerprint isn't explicitly given, providing the end_time generates a new Alert, since aren't excluding the end_time from the payload when generating the fingerprint.

We should ignore the end_time like we currently do for start_time, and hosts.