[ML] Add daily task to manage .ml-state indices

[edsavage]

Add a daily maintenance task to roll over .ml-state indices if the index size exceeds a configurable default size (default 50GB).

This replaces the previous method of using ILM to manage the state indices, as that was not a workable solution for serverless.

This builds on the work done in PR #136065 which provides similar functionality for results indices.

[github-actions]

🔍 Preview links for changed docs

• docs/reference/elasticsearch/configuration-reference/machine-learning-settings.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]

Hi @edsavage, I've created a changelog YAML for you.