Do not reload application routes before eager loading

What does this MR do?

This should speed up the booting of the application by 3-4 seconds with the eager_load option set as true.

Why?

Because Rails is already loading the routes after the eager loading process with the set_routes_reloader_hook. Since there is no way to disable this without applying a dirty patch, we should instead disable loading the routes with Devise before the eager_load hook. Since we have a relatively big amount of route definitions, running this twice adds an extra ~4 seconds to the booting process.

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
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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