Show function hints when selecting a native histogram

[bohandley]

The query editor will provide hints for classic histogram metrics by showing the function histogram_quantile. But, when a user selects a native histogram, none of the native histogram functions are shown as hints.

Classic histogram

Native histogram

Native histogram function hints should include
histogram_avg no documentation link yet, just merged: prometheus/prometheus#13467
histogram_count
histogram_sum
histogram_fraction
histogram_stddev
histogram_stdvar

How to differentiate classic and native?

If we know a metric is of a certain type, we can show a hint.

Currently there is no metadata available for native histograms so we have little to differentiate them from classic. (See grafana/alloy#547).

We know classic histograms always end in _bucket, _sum, or _count like
cortex_request_duration_seconds_bucket

And a native histogram metric would have everything but the suffix.
cortex_request_duration_seconds

One suggestion is that if we know there is a classic histogram available, we can identify it, remove the suffix and create a collection of native histogram metric names. We could then compare any selected metric to that collection to identify it as a native histogram. This is not as nice as simply checking the metadata for the type, but it is one idea.

*update: The above idea will not work because classic histograms will be removed and there will be nothing to compare native histograms to.

What we are left with is a metric name with no clear frontend way to identify it's type. Another solution is to create a resource-like call that queries a chosen metric and parses the response to identify the metric as a native histogram, then return this information to the frontend to provide the hint. This would not be scalable to apply to all metrics but it could provide us the hint.

**Additional update: use metadata and test with vanilla Prometheus see slack for more context https://raintank-corp.slack.com/archives/C02UC0KCSF4/p1713424061722829?thread_ts=1708519355.394509&cid=C02UC0KCSF4

We discussed this with Beorn yesterday and the best information and API currently is the metadata endpoint. If it has the type==histogram and the series doesn't end in _bucket, _count or _sum, you can be reasonably sure that it is a native histogram.

[bohandley]

PR enables these hints