[ES|QL] Publish command status as JSON

[drewdaemon]

Description

The ES|QL editor needs to know whether commands have been released (snapshot-only) and whether they are in tech preview or not. Right now this relies on cross-team communication which is not foolproof.

Our proposal is to give control to Elasticsearch much like we do with the function definitions. Each command can have a corresponding JSON file which could look something like the following:

{
  "name": "LOOKUP JOIN",
  "preview" : true,
  "snapshot_only" : false,
  "docs_markdown": "..."
}

We can scrape this metadata in our weekly CI job and update the editor behavior for each command.

Including the docs would be nice because that would allow them to be automatically added to the editor's inline documentation, just as the functions are today.

cc @nik9000 for a feasibility check.

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[elasticsearchmachine]

Pinging @elastic/kibana-esql (ES|QL-ui)