Geo - Does not redirect user to the custom home page URL on a Geo secondary

What does this MR do?

If a user is not signed-in and tries to access root_path on a Geo secondary node, it redirects him to the sign-in page. Don't redirect to the custom home page URL if it is one is set. Otherwise, it will break the Geo OAuth workflow always redirecting the user to the Geo primary node, which prevents access to the secondary node.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance 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

Related issues

Closes #11594 (closed)