When opening Web IDE, follow path to fork if it exists

What does this MR do?

Issue: #202159 (closed)

Currently when a user doesn't have permissions to commit or create a merge request in a project we offer the user the option to fork the project when opening the Web IDE. However, if a user already has a fork then we open the upstream project and not the forked project in the Web IDE. This means users are "doomed to fail" as they won't be able to make changes, or save their changes and make them in the appropriate context.

Screenshots

Before	After

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