receiver/promettheusreceiver: add option to the metric adjuster to fallback to collector start time

[ridwanmsharif]

Component(s)

receiver/prometheusreceiver

Is your feature request related to a problem? Please describe.

When scraping prometheus metrics, there often are no start times associated with the cumulative metrics. There is a metric adjuster that allows the configurer to specify another metric name from which to pull start time for all metrics scraped but I believe its useful to have a fallback mechanism to fall back to the collector start time.

This is useful especially in serverless workloads or workloads where the collector runs as a sidecar to the target being scraped. We currently use this approach for Cloud Run observability in https://github.com/GoogleCloudPlatform/run-gmp-sidecar/ and its been very useful there.

Describe the solution you'd like

An option added to the config, something like UseCollectorStartTimeFallback

Describe alternatives you've considered

No response

Additional context

No response

[github-actions[bot]]

Pinging code owners for receiver/prometheus: @Aneurysm9 @dashpole. See Adding Labels via Comments if you do not have permissions to add labels yourself. For example, comment '/label priority:p2 -needs-triaged' to set the priority and remove the needs-triaged label.

[dashpole]

cc @ArthurSens