Resolve "Follow up - Migrate mock data to fixture spec"

What does this MR do?

We introduced some hard coded mock data in !15216 (merged) while waiting for the relevant backend to be completed, now that it has been implemented in !16240 (merged) we should generate the mock data from a fixture spec as per our frontend testing guide

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

Removes ~194 lines of hard coded mock data

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

Closes #32112 (closed)