Adding docs-producing tests for delta, idelta, increase, irate

[pabloem]

Adding tests that validate functionality of new esql functions. These tests, upon passing, generated markdown and other files of documentation that are included for kibana and es.

[github-actions]

🔍 Preview links for changed docs

• docs/reference/query-languages/esql/kibana/docs/functions/delta.md
• docs/reference/query-languages/esql/kibana/docs/functions/idelta.md
• docs/reference/query-languages/esql/kibana/docs/functions/increase.md
• docs/reference/query-languages/esql/kibana/docs/functions/irate.md

[github-actions]

ℹ️ Important: Docs version tagging

👋 Thanks for updating the docs! Just a friendly reminder that our docs are now cumulative. This means all 9.x versions are documented on the same page and published off of the main branch, instead of creating separate pages for each minor version.

We use applies_to tags to mark version-specific features and changes.

Expand for a quick overview

When to use applies_to tags:

✅ At the page level to indicate which products/deployments the content applies to (mandatory)
✅ When features change state (e.g. preview, ga) in a specific version
✅ When availability differs across deployments and environments

What NOT to do:

❌ Don't remove or replace information that applies to an older version
❌ Don't add new information that applies to a specific version without an applies_to tag
❌ Don't forget that applies_to tags can be used at the page, section, and inline level

🤔 Need help?

• Check out the cumulative docs guidelines
• Reach out in the #docs Slack channel

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)

[elasticsearchmachine]

Pinging @elastic/core-docs (Team:Docs)

[leemthompo]

noticed couple things driving by here :)

[leemthompo]

a null example will break Kibana, @ioanatia just added a check for this in #135094

[pabloem]

fixed!

[leemthompo]

these functions needs to have the correct version info

stack: preview|ga 9.2.0

see https://github.com/elastic/elasticsearch/tree/main/docs/reference/query-languages/esql#version-differentiation-in-docs-v3

[kkrik-es]

#134373 addresses this, please sync and rerun tests to regen.

[pabloem]

rebased!

[leemthompo]

@pabloem delta still has stack:unavailable while the others have been updated

[pabloem]

oops added!

[leemthompo]

Delta still has incorrect version info and the examples are null for all 4 functions. We can't have null examples per #135094.

Maybe just need to merge main at this point and regenerate, not sure :)

[leemthompo]

@pabloem delta still has stack:unavailable while the others have been updated

[dnhatn]

I left some smaller comments, but LGTM. Thanks @pabloem