prometheusbp: add support for native histograms

[Xaelias]

💸 TL;DR

Add support for native histograms using the following settings:

• NativeHistogramBucketFactor: 1.1
• NativeHistogramMaxBucketNumber: 160
• NativeHistogramMinResetDuration: 1h

Jira

This changes means that all histograms defined in baseplate.go will now be scraped as native histograms if the service is scraped using the PrometheusProto protocol. This also requires the resulting prometheus instance to be configured to accept native histograms.

If the service is scraped using plantext (the default), then the existing classic histograms will be scraped and this change doesn't change anything for the resulting metrics.

NB:

• services will keep track of BOTH classic and native histograms while both buckets and these 3 settings are set at the same time
• if a namespace is configured to scrape using protobuf, but native histogram support is not explicitly enabled, neither the classic or native histograms will be scraped.

🧪 Testing Steps / Validation

✅ Checks

• CI tests (if present) are passing
• Adheres to code style for repo
• Contributor License Agreement (CLA) completed if not a Reddit employee