Fix issue with frames not loading in Safari

Merged Dominic Couture requested to merge fix-safari-child-src into master

What does this MR do?

Fixes #331692 (closed)

In CSP level 3 the frame-src directive is to be prioritized over child-src but apparently Safari doesn't follow that so we're going to keep both of those values equal until browsers standardize.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

Availability and Testing

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

  • Label as security and @ mention @gitlab-com/gl-security/appsec
  • The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
  • Security reports checked/validated by a reviewer from the AppSec team
Edited by Dominic Couture