Remove 1h backfilling limitation

[joaogbcravo]

Summary: Remove the limitation "Metric samples older than 1 hour are refused from being ingested" as stated at https://docs.aws.amazon.com/prometheus/latest/userguide/AMP_quotas.html

There is at least a similar issue like this one #18

However, our use case is different. I don't want to simply do a migration from one database to AMP (although that would also be important). We want to be able to send metrics at any time, despite how old they are.

We work with edge devices that, from time to time, are not connected to the internet. Those edge devices, when not connected to the internet and therefore unable to push the metrics, keep them on a local cache. As soon as they have an internet connection, they should be able to push that cache (sometimes older than 1h, 1 day, or in rare cases 1 week) to AMP.

This 1-hour limitation seems to be just a particular AMP limitation. At the moment, this is a blocker for our edge devices to use AMP, and therefore we keep using a self-managed Prometheus.