Migrate otel metrics to use mdatagen

[codeboten]

Component(s)

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Describe the issue you're reporting

In an effort to improve consistency in naming and discoverability of the telemetry emitted by Collector components, metrics are being defined in a component's metadata.yaml file, which is then used by mdatagen to generate telemetry code and documentation.

This functionality will allow future changes that require updating of all internal telemetry to be applied more easily. The following components still need updating:

• Migrate otel metrics to use mdatagen: statsd receiver #33524
• Migrate otel metrics to use mdatagen: routing processor #33526
• Migrate otel metrics to use mdatagen: deltatocumulative processor #33573
• Migrate otel metrics to use mdatagen: receiver/otelarrow #33666
• Migrate otel metrics to use mdatagen: splunkhec exporter #33985
• migrate otel metrics to use mdatagen: internal/otelarrow #34135