[Internal]: Add info about minimum ML node sizing requirements in security docs

[dhru42]

Description

What: In order to use ELSER, users must deploy it on an ML node to ensure that the model has enough resources. Given that security users also use ELSER, we should explicitly document this in our security docs. Otherwise, add a clear reference link to ELSER docs.

Resources

To use ELSER, the NLP model must be deployed in your Elasticsearch cluster. The minimum dedicated ML node size for deploying ELSER is 4 GB, with autoscaling recommended for dynamic resource adjustment.

Reference discussion: https://elastic.slack.com/archives/C05BAPPP5KP/p1747718012584609

Which documentation set does this change impact?

Elastic On-Prem and Cloud (all)

Feature differences

adding compute requirements references for users

What release is this request related to?

8.17

Serverless release

ASAP

Collaboration model

The documentation team

Point of contact.

Main contact: @dhru42

Stakeholders: @jamesspi