Bump go.opentelemetry.io/collector/config/configopaque from 0.80.0 to 1.21.0 in /exporter/prometheusremotewriteexporter

Bump go.opentelemetry.io/collector/config/configopaque from 0.80.0 to 1.21.0 in /exporter/prometheusremotewriteexporter #15873