update OOTB OTel Collector dashboard to use semantic mode: combined (DataDog#20773)

* update OOTB OTel Collector dashboard to use semantic mode: combined

* json formating

* update OTel host metrics dashboard

* fix network metric queries

* Update otel/assets/dashboards/otel_host_metrics_dashboard.json

Co-authored-by: Yang Song <songy23@users.noreply.github.com>

* Update otel/assets/dashboards/otel_collector_metrics_dashboard.json

Co-authored-by: Yang Song <songy23@users.noreply.github.com>

* add back read_only flag that was accidentally removed

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Co-authored-by: Yang Song <songy23@users.noreply.github.com>

Author: shanelhuang