[Security][8.18] Implement a Public API for Assistant Knowledge Base

[benironside]

Description

With the launch of the custom knowledge feature for the assistant in 8.16, we did not provide any public APIs for CRUD operations on knowledge entries, however, we did implement a set of internal apis.

This epic is to track to work to create a public version of those APIs, to allow users to make programmatic changes to knowledge base entries.

https://github.com/elastic/security-team/issues/11365

Resources

More details here: https://github.com/elastic/security-team/issues/11365

Which documentation set does this change impact?

Elastic On-Prem and Cloud (all)

Feature differences

What release is this request related to?

8.18

Collaboration model

The documentation team

Point of contact.

Main contact: @Charelzard

Stakeholders: