Add ability to run reactive caching synchronously

What does this MR do?

Occasionally I find myself needing to debug work that happens inside a reactive cache calculation. Usually I would hop into pry but these reactive cache calculations occur in the worker thread and prying there is not easy. This MR introduces a new method without_reactive_caching that performs the calculations in the main server thread instead of sidekiq.

In order to make sure we don't forget to switch without_reactive_caching back to with_reactive_caching after debugging, I've added an additional cop here: https://gitlab.com/gitlab-org/gitlab-styles/merge_requests/33

Note: We will need to bundle update to make sure we are pulling in the updated gitlab-styles gem once the above MR is merged. This MR has been updated to include the new gitlab-styles version.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• 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