update batch processors to emit otel semconv metrics

[brettmc]

Our SDK's BatchSpanProcessor and BatchLogRecordProcessor emit metrics about their internal state, eg otel.trace.span_processor.spans and otel.logs.log_processor.queue.usage. Since #1633 has been merged we have some official semantic conventions that can be used.

We should:

• use semconv where available
• consider dropping or submitting new semconv's for metrics we emit that do not map to a semconv

See https://opentelemetry.io/docs/specs/semconv/otel/sdk-metrics/

This is not a breaking change in terms of API, but behaviourally different enough to go into SDK 2.x ?

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