Change log "stream' attribute according to OTel semantic conventions

Rename `stream` log attribute to `log.iostream` according to [OTel semantic conventions](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/logs/semantic_conventions/media.md#io-stream)

helm-charts/splunk-otel-collector/templates/config/_otel-agent.tpl

@@ -209,7 +209,7 @@ receivers:
           k8s.pod.name: 'EXPR($$.pod_name)'
           com.splunk.sourcetype: 'EXPR("kube:container:"+$$.container_name)'
         attributes:
-          stream: 'EXPR($$.stream)'
+          log.iostream: 'EXPR($$.stream)'
       {{- if .Values.logsCollection.containers.multilineConfigs }}
       - type: router
         routes: