Add support for non exhaustive variants

[swallez]

Elasticsearch plugins can add new implementations for a significant number of components, such as for example queries, aggregations and property types.

This PR adds an additional @non_exhaustive annotation (term borrowed from Rust's equivalent feature) that can be added to @variants types and enums (see below) to capture the fact that variants or enum members not present in the spec can exist, and clients should allow that.

This PR also adds the new @non_exhaustive annotation to the relevant types, found from the plugin interface definitions in the ES code base.

Example:

/**
 * @variants container
 * @non_exhaustive
 */
export class QueryContainer {
  ...
}

The following pluggable components were left out from this PR as they require a bit more investigation in their specification: highlighters, score functions, significance heuristics.

enums: for consistency this PR also changes @open_enum for open enumerations to @non_exhaustive. The enum metamodel isn't changed, and this annotation still sets the isOpen property.

Related: Java implementation of @non_exhaustive: elastic/elasticsearch-java#252

[github-actions]

Following you can find the validation results for the APIs you have changed.

API	Status	Request	Response
ingest.delete_pipeline	🟢	11/11	11/11
ingest.geo_ip_stats	⚪	Missing test	Missing test
ingest.get_pipeline	🟢	22/22	22/22
ingest.processor_grok	🟢	1/1	1/1
ingest.put_pipeline	🟢	30/30	30/30
ingest.simulate	🟢	4/4	4/4
search	🔴	1492/1526	1505/1508

You can validate these APIs yourself by using the make validate target.

[sethmlarson]

This is super great, love what's been done with @open_enum to make everything even more consistent!

[github-actions]

The backport to 7.17 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-7.17 7.17
# Navigate to the new working tree
cd .worktrees/backport-7.17
# Create a new branch
git switch --create backport-1662-to-7.17
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick --mainline 1 7c3d1ce0febc9d78d7e385bf5ec503fb5e3af1e1
# Push it to GitHub
git push --set-upstream origin backport-1662-to-7.17
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-7.17

Then, create a pull request where the base branch is 7.17 and the compare/head branch is backport-1662-to-7.17.