[ES|QL] [Unified histogram] Add a breakdown dropdown to the ES|QL histogram

[stratoula]

Describe the feature:

We want to give the users the ability to create breakdowns in ES|QL histogram mode. We decided to not go with inlinestats but keep the stats implementation and add a breakdown in the histogram component (exactly as in dataview mode) that it will update the underlying query on field selection

The latter is very important for the OneDiscover project. If we have the context, we want programmatically to breakdown the histogram with a specific field defined by the Discover app. We can't do it without inline stats support

[elasticmachine]

Pinging @elastic/kibana-esql (Team:ESQL)

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[kertal]

@stratoula @ninoslavmiskovic I've got a question about the breakdown by log levels using ES|QL. In Lens / data view mode using Breakdown / Filters we can group terms like error,Error,Err, into error by using one filter, with colors by terms mapping we can assign the right color for the severity. Is there a way to do this in ES|QL?

Context: #186273

[stratoula]

@kertal sorry what do you mean with by using one filter?

with colors by terms mapping we can assign the right color for the severity. --> yes of course

Update: I see now what you mean. Yes we will be able to do so (with inlinestats and the case function). This is why I added this task to our team, it is better if we take the query construction part. From the moment we have the breakdown field then the color mapping works the same as in the dataview mode.

[kertal]

@stratoula great thx! Out of curiosity, how will and ES|QL query for something like this look like?

[stratoula]

It will be quite complex, I need inlinestats first to be sure how it will look like. Patience!

[stratoula]

First step is this PR #189630 (it just replaces stats with inlinestats) on the histogram query enabling the rest of the fields to be present in the inline editing breakdown. I am not releasing this yet because inhlinestats is still only present on snapshots releases (this is why the tests are failing)

[stratoula]

Second step is this PR #190213 where it initializes the histogram with the log.level column if it exists.

This is blocked by the fact that we would like to order the bars and legend by severity but this doesnt seem possible now at Lens. cc @MichaelMarcialis

@nickofthyme we had discussed it, not sure if you discussed it with the team and can give us an update here. cc @elastic/kibana-visualizations

[stratoula]

The first part got merged #193820. This enables the breakdown from the histogram.

The next part is to initialize the breakdown by log.level. We discussed it with the @elastic/kibana-data-discovery team and they are going to take it. With that being said, I am closing this issue and will create a new one to track the one discover requirement