Update CORS documentation for stricter Safari handling

[jazzsequence]

Re: Create a WordPress MU-Plugin for Actions and Filters: Cross-Origin Resource Sharing (CORS)

Priority: Medium

Issue Description

A customer requested for an additional note regarding CORS issues on Safari in this doc

Safari has stricter rules compared to chromium-based browser, which leads to CORS issues only there (reference here). The customer is aware of the scope of the issue, and stated it would be helpful if an additional note mentions that CORS issues may continue in certain browsers even if the correct steps are followed.

Suggested Resolution

• Update the doc to note Safari rules.
• If it's possible to suggest a solution/alternative, we should document that, too. May require SME to validate.