[ES|QL] don't suggest snapshot-only functions

[drewdaemon]

We should not suggest functions that are only available on Elasticsearch snapshots. However, we should accept them if the user types them (not throw validation errors).

We should also exclude snapshot-only functions from the inline docs

Technical plan

With elastic/elasticsearch#113544, Elasticsearch will be adding the snapshot_only property to function definitions. When generating function definitions on our side, snapshot_only should be interpreted as our ignoreAsSuggestion function definition property (and we have to make that work for all function types because it is currently only in use for operators).

[elasticmachine]

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

[stratoula]

@drewdaemon can we prioritize it for 8.16?

[drewdaemon]

@stratoula absolutely. It is one of the next things I will do.

[drewdaemon]

Or, we could always be smarter about this and use the cluster response to detect whether Kibana is pointed at a snapshot cluster...

{
  "name" : "MacBook-Pro.local",
  "cluster_name" : "elasticsearch",
  "cluster_uuid" : "SHmCgXLjSWSTx1GqTROykw",
  "version" : {
    "number" : "8.15.0-SNAPSHOT",
    ...
    "build_snapshot" : true,
  },
  "tagline" : "You Know, for Search"
}

That way, we could suggest these functions on snapshots and pretend like they don't exist on non-snapshots. Feels a bit cleaner. WDYT @stratoula

[stratoula]

Interesting idea. How can we get the cluster info?

[drewdaemon]

GET <cluster-url>:9200

[drewdaemon]

Looks like we already do it for telemetry collection:

https://github.com/elastic/kibana/blob/main/src/plugins/telemetry/server/telemetry_collection/get_cluster_info.ts#L20

But, esClient is only server-side so we'd probably need an ES|QL endpoint

[stratoula]

I was expecting that, I am not sure if it is worth it (I mean to create an endpoint and do an extra call). I think using the ES preview is enough. I don't think we are gaining a lot unless I am missing something.

[drewdaemon]

@stratoula makes sense, but I thought we were creating an endpoint anyways, so this could be something to keep in our back pocket. I don't think this will the be the last time the idea of having the editor react to state from the Elasticsearch cluster will come up (e.g. feature flags, version upgrades, custom functions).

[stratoula]

@drewdaemon totally, we are def keeping it as an idea.

[drewdaemon]

Blocked on elastic/elasticsearch#113544

[drewdaemon]

Unblocked!