otelcol.connector.spanmetrics should support the metrics_expiration option

[madaraszg-tulip]

Request

Currently the spanmetrics connector never stops feeding stale metrics.

The upstream code has recently implemented the metrics_expiration option, it would be great if grafana-agent could make use of it.

open-telemetry/opentelemetry-collector-contrib#31106

Use case

We would like to keep our cardinality lower by not feeding metrics which we consider stale.

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