Add custom cop to prevent permissions enabling permissions

What does this MR do and why?

This MR adds a custom rubocop cop that identifies instances of permissions enabling other permissions.

References

https://gitlab.com/gitlab-org/gitlab/-/issues/523519

How to set up and validate locally

Checkout the branch and run rubocop on any policy. Ex:

rubocop app/policies/project_policy.rb

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.