nagios_xi using invalid field values according to ECS

[jsoriano]

[0] parsing field value failed: field "event.kind"'s value "events" is not one of the allowed values (alert, enrichment, event, metric, state, pipeline_error, signal)[0] parsing field value failed: field "event.kind"'s value "metrics" is not one of the allowed values (alert, enrichment, event, metric, state, pipeline_error, signal)
"events" => "event""metrics" => "metric"

Part of #3016

[jsoriano]

Reopening as there seems to be still some issue:

one or more errors found in documents stored in logs-nagios_xi.service-ep data stream: [0] parsing field value failed: field "event.kind"'s value "metrics" is not one of the allowed values (alert, enrichment, event, metric, state, pipeline_error, signal)

Seen in https://beats-ci.elastic.co/blue/organizations/jenkins/Ingest-manager%2Fintegrations/detail/PR-3017/3/tests