[SEMCON-748] fix DD exporter and connector metrics on OTel collector dashboard

[songy23]

What does this PR do?

Fix DD exporter and connector APM related metrics on OTel collector dashboard

Motivation

• https://datadoghq.atlassian.net/browse/SEMCON-748 Filter internal APM health metrics (otelcol_datadog_trace_agent_* metrics) by source:datadogexporter, only metrics with this tag are indeed from DD exporter or connector.
  • Note most metrics from DD connector also have source:datadogexporter rather than source:datadogconnector because metrics are sent with DD exporter.
• https://datadoghq.atlassian.net/browse/OTAGENT-44 Add deprecation notice to traces/s and spans/s metrics on the DD connector section. Those 2 metrics no longer apply when native ingest in DD connector is enabled, in that case traces go through the new OTel stats API rather than the OTLP receiver in trace agent.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

Review from steveny91 is dismissed.
Related teams and files:

• agent-integrations
  • otel/assets/dashboards/otel_collector_metrics_dashboard.json
    Review from mx-psi is dismissed.
    Related teams and files:
• opentelemetry
  • otel/assets/dashboards/otel_collector_metrics_dashboard.json

[songy23]

Fixed a typo, could you take another look? @steveny91 @mx-psi