[REQUEST]: Add csp.report_only.object_src directive to the documentation

[elena-shostak]

Description

csp.report_only.object_src: Add sources for the Content Security Policy object-src directive in reporting mode.

Resources

This feature was implemented in elastic/kibana#209306

Which documentation set does this change impact?

Elastic On-Prem and Cloud (all)

Feature differences

The feature is identical in all deployments

What release is this request related to?

9.0

Collaboration model

The engineering team

Point of contact.

Main contact: @elena-shostak

Stakeholders: @elastic/kibana-security

[georgewallace]

@wajihaparvez Can you take a look at this?