Make Kuery work with multiple index patterns

[timroes]

Currently the toElasticsearchQuery expects to get one index pattern passed into it, when trying to convert Kuery into a ES query.

That's why currently TSVB, timelion and Vega don't work with Kuery (see #17722), because all of those visualizations do actually support using multiple (or none) index pattern at all.

I think we really should support a new query language for all visualizations, and not just a couple of them on a dashboard, since that will be very unintuitive for the user. Therefor we need to make Kuery also work with multiple index-pattern or none at all.

cc @elastic/kibana-discovery

[Bargs]

Or: TSVB, Timelion and Vega should use index patterns like the rest of Kibana. It's a discussion we can have, but KQL relies on index patterns for both scripted fields and wildcard field names. It would be equally weird if these features just broke on the affected visualizations.

[timroes]

Okay maybe I described that a bit confusing. Timelioe and Vega already understand index patterns and timelion already load them for scripted fields. The problem is, that we could potentially query against different index patterns in one chart. But I think I understand your answer that we should rather try to convert kql for each index pattern individually? (Like deeper down in the implementation)

[Bargs]

Let's zoom about it some time, I'm not 100% sure if we're on the same page but from what you just said I'm thinking it may not be too difficult.

[timroes]

After syncing offline about that, I can close this. Kquery should always require an index pattern. In places where a visualization can have multiple index patterns (like timelion) we also need to issue multiple requests (or bundle them in an _msearch request), so we should simply compile Kquery for all those individual requests and their respective index patterns.