Enable sharding for avg_over_time.

[jeschkies]

What this PR does / why we need it:
The range aggregation avg_over_time is simply shardable if there's no label reduction.

If there is one it can be express as

sum by (method) (
    sum_over_time(
        {container="app"} | json | unwrap bytes [$__interval])
) 
/
sum by (method) (
    count_over_time(
        {container="app"} | json [$__interval]
    )
) 

Note that sum by, sum_over_time and count_over_time are shardable once more.

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• CHANGELOG.md updated
  • If the change is worth mentioning in the release notes, add add-to-release-notes label
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• For Helm chart changes bump the Helm chart version in production/helm/loki/Chart.yaml and update production/helm/loki/CHANGELOG.md and production/helm/loki/README.md. Example PR

[owen-d]

Nice. Left a nit, but lgtm

[owen-d]

Will be more extensible if we Clone(self) then set the unwrap to nil. This ensures that any future fields are propagated through this function.

[jeschkies]

Unfortunately it returns and unexpected unwrap error. I'll take a look tomorrow.

[cstyan]

awesome!

[cstyan]

is this correct? unwrapbusy missing a space?

[cstyan]

and jsonbusy?

[jeschkies]

We remove all white spaces in the tests. I've copied the expected string and adapted. Will fix.

[jeschkies]

Done.

[cstyan]

for something like avg(avg_over_time({job=~"myapps.*"} |= "stats" | json busy="utilization" | unwrap busy [5m])) is the unwrap part of the left? And then the inner avg_over_time is the right?

[jeschkies]

You mean in parsing? It has its own field 🙈