[ES\QL] Add a section for vector functions in the doc.

[afoucret]

There are no section for vector functions in the reference doc.

Added one.

[elasticsearchmachine]

Pinging @elastic/es-search-relevance (Team:Search Relevance)

[elasticsearchmachine]

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

[carlosdelest]

Besides knn, the other functions are not out of snapshot yet - let's remove them, or add them commented out similar to raw.githubusercontent.com/elastic/elasticsearch/0363570e9df2eac6c40a89b418c340acc2450258/docs/reference/query-languages/esql/functions-operators/search-functions.md

[leemthompo]

We shouldn't include the knn docs twice, because this would be bad for SEO, as we'd have duplicate pages in the docs. We should pick one page (vector functions), include it there, and link there from the other.

[github-actions]

🔍 Preview links for changed docs

• docs/reference/query-languages/esql/functions-operators/dense-vector-functions.md
• docs/reference/query-languages/esql/esql-functions-operators.md
• docs/reference/query-languages/esql/functions-operators/search-functions.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

[leemthompo]

couple minor comments/suggestions

[carlosdelest]

LGTM, thanks for taking care of this @afoucret !

[leemthompo]

@afoucret in Knn.java, the applies_to needs to be updated with version. On line 106::

--- appliesTo = { @FunctionAppliesTo(lifeCycle = FunctionAppliesToLifecycle.PREVIEW)
+++ appliesTo = { @FunctionAppliesTo(lifeCycle = FunctionAppliesToLifecycle.PREVIEW, version = "9.2.0")

[leemthompo]

👍 thanks for iterating so fast, I couldn't keep up 😁