Combine es and ese search strategies

[timroes]

We currently have an es strategy (the old OSS strategy), which can only request data via _search and the ese search strategy, which supports async search and rollups. I feel this is a bit of a weird (most likely historical grown mix), since e.g. if you're using the es strategy to not get async search you'd automatically also lose access to querying rollup.

I wanted to discuss if it could be worth merging those two into one es search strategy, where async search and rollup support would simply be available parameters to turn it off or on. I feel that way it might be easier to maintain them in the future, especially if we'll start adding support for other features into them.

[timroes]

cc @lukasolson @ppisljar

[Dosant]

Not sure what is the plan about merging the strategies, but at some point, we thought of moving rollup search into its own strategy #98122

[timroes]

The problem that I'd see about that (but I could have a false understanding here): The consumer of the API needs to select the strategy, meaning whoever wants to use a search strategy then would suddenly need to do a check: is the index pattern rollup, if so get a different search strategies and request it. That makes imho consumption of the search service significantly more complex. Looking through the PR you linked it seems we're currenlty doing that in SearchSource, but that might just be one place, and all direct consumers of the Search Service will suddenly need to repeat that logic all over the place. I am a bit concerned if that really makes that service better to consume and if it's not better combining search strategies and just have them determine those differences they can detect automatically internally.

[elasticmachine]

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

[kertal]

Closing this because it's not planned to be resolved in the foreseeable future. It will be tracked in our Icebox and will be re-opened if our priorities change. Feel free to re-open if you think it should be melted sooner.