[ES|QL] Add support for counters to First/LastOverTime

[limotova]

This commit adds support for running FirstOverTime and LastOverTime on counter fields (counter_long, counter_integer, counter_double).

The return value is the non-counter variation.
For example, the following is a valid query and will return a double:

TS my_tsdb
| STATS max(first_over_time(my_counter_double_field))
  BY my_dimension, bucket(@timestamp, 10minute)

[elasticsearchmachine]

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

[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

[dnhatn]

Are we sure we want over_time to work with counter fields? We have intentionally restricted counter fields to only rate and explicit casting.

[kkrik-es]

I think we do, to support something like:

TS metrics | STATS requests

TS metrics | STATS max(requests) BY TBUCKET(5m)

[dnhatn]

I am on the fence about adding this support, but if Kostas needs it, I am okay with it. LGTM, thanks Larisa!

[limotova]

This build was successful, just status not reported, so I am merging this