[REQUEST][Security]: New sub-feature priv for case assignees

[nastasha-solomon]

Description

Am introducing a new cases assignee sub-feature priv that will allow users to control a role's ability to change the assignee of a case. When the priv is enabled, they can assign any user to any case. When it's disabled, the assignees component is hidden in the UI. See the linked PR for screenshots.

Resources

Feature implemented in elastic/kibana#201654.

Which documentation set does this change impact?

Elastic On-Prem and Cloud (all)

Feature differences

N/A

What release is this request related to?

9.0 (Still unsure whether this made it into 8.18)

Collaboration model

The documentation team

Point of contact.

Main contact: @kqualters-elastic

Stakeholders: @paulewing

[kqualters-elastic]

"When it's disabled, the assignees component is hidden in the UI. See the linked PR for screenshots."

I would also just add something about the API returning forbidden as well, something like:

"When it's disabled, the assignees component is hidden in the UI, and the API returns a permission not allowed error if any case in the update request has a new status."