prometheusreceiver: Make use of created timestamp from prometheus

[dashpole]

Component(s)

receiver/prometheus

Describe the issue you're reporting

Prometheus now parses the timestamp for us: prometheus/prometheus#14356. We need to implement the CreatedTimestampAppender interface (with the AppendCTZeroSample method and AppendHistogramCTZeroSample methods) to get access to it.

We also need to set EnableCreatedTimestampZeroIngestion to true in the scrape manager for the AppendCT* methods to be called.

We should remove the receiver.prometheusreceiver.UseCreatedMetric feature gate, and associated code after this is complete.

cc @open-telemetry/wg-prometheus

[dashpole]

cc @ridwanmsharif
since you are also interested in created timestamp support