cisco_ftd, cisco_duo using invalid values according to ECS

```
[0] parsing field value failed: field "event.outcome"'s value "failed" is not one of the allowed values (failure, success, unknown)
[0] parsing field value failed: field "event.outcome"'s value "monitored" is not one of the allowed values (failure, success, unknown)
```
Related to https://github.com/elastic/integrations/issues/3016