Fix the URL generation for feature flags

What does this MR do?

This fixes a bug where the URL generated for feature flags is incorrect (see: #299424 (closed)).

This is due to a typo of id for iid. This is fixed to use the routing methods.

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.