[mdatagen] support linking to helper telemetry

[codeboten]

Individual components now provide details about the telemetry they emit https://github.com/open-telemetry/opentelemetry-collector/blob/main/processor/batchprocessor/documentation.md#internal-telemetry. However, the documentation produce doesn't include telemetry offered by helper packages https://github.com/open-telemetry/opentelemetry-collector/blob/main/processor/processorhelper/documentation.md#internal-telemetry.

It would be great if mdatagen either included the telemetry in the component documentation or at the very least linked to the helper's documentation